Systems and methods for controlling the temperature of a vapor deposition apparatus

ABSTRACT

The present invention provides systems, methods and apparatus for high temperature (at least about 500-800° C.) processing of semiconductor wafers. The systems, methods and apparatus of the present invention allow multiple process steps to be performed in situ in the same chamber to reduce total processing time and to ensure high quality processing for high aspect ratio devices. Performing multiple process steps in the same chamber also increases the control of the process parameters and reduces device damage. In particular, the present invention can provide high temperature deposition, heating and efficient cleaning for forming dielectric films having thickness uniformity, good gap fill capability, high density, low moisture, and other desired characteristics.

This application is related to concurrently filed and commonly assignedU.S. patent application Ser. No. 08/749,283 entitled "HEATER/LIFTASSEMBLY FOR HIGH TEMPERATURE PROCESSING CHAMBER," having JonathanFrankel, Hari Ponnekanti, Inna Shmurun, and Visweswaren Sivaramakrishnanlisted as co-inventors (filed on Nov. 13, 1996); and to concurrentlyfiled and commonly assigned U.S. patent application Ser. No. 08/746,748entitled "CHAMBER LINER FOR HIGH TEMPERATURE PROCESSING CHAMBER," havingJonathan Frankel and Visweswaren Sivaramakrishnan listed asco-inventors; and to concurrently filed and commonly assigned U.S.patent application Ser. No. 08/747,830 entitled "SUBSTRATE PROCESSINGAPPARATUS WITH BOTTOM-MOUNTED REMOTE PLASMA SYSTEM," having Gary Fongand Irwin Silvestre listed as co-inventors; and to concurrently filedand commonly assigned U.S. patent application Ser. No. 08/749,284entitled "LIFT ASSEMBLY FOR HIGH TEMPERATURE PROCESSING CHAMBER," havingJonathan Frankel listed as inventor; and to concurrently filed andcommonly assigned U.S. patent application Ser. No. 08/749,286 entitled"SYSTEMS AND METHODS FOR DETECTING END OF CHAMBER CLEAN IN A THERMAL(NON-PLASMA) PROCESS," having Visweswaren Sivaramakrishnan and Gary Fonglisted as co-inventors; and to concurrently filed and commonly assignedU.S. patent application Ser. No. 08/749,925 entitled "LID ASSEMBLY FORHIGH TEMPERATURE PROCESSING CHAMBER," having Jonathan Frankel, InnaShmurun, Visweswaren Sivaramakrishnan, and Eugene Fukshanski listed asco-inventors; and to concurrently filed and commonly assigned U.S.patent application Ser. No. 08/748,095 entitled "METHODS AND APPARATUSFOR CLEANING SURFACES IN A SUBSTRATE PROCESSING SYSTEM," having GaryFong, Li-Qun Xia, Srinivas Nemani, and Ellie Yieh listed asco-inventors; and to concurrently filed and commonly assigned U.S.patent application Ser. No. 08/747,982 entitled "METHODS AND APPARATUSFOR GETTERING FLUORINE FROM CHAMBER MATERIAL SURFACES," having Li-QunXia, Visweswaren Sivaramakrishnan, Srinivas Nemani, Ellie Yieh, and GaryFong listed as co-inventors; and to concurrently filed and commonlyassigned U.S. patent application Ser. No. 08/748,960 entitled "METHODSAND APPARATUS FOR DEPOSITING PREMETAL DIELECTRIC LAYER ATSUB-ATMOSPHERIC AND HIGH TEMPERATURE CONDITIONS," having Li-Qun Xia,Ellie Yieh, and Srinivas Nemani listed as co-inventors; and toconcurrently filed and commonly assigned U.S. patent application Ser.No. 08/746,631 entitled "METHODS AND APPARATUS FOR SHALLOW TRENCHISOLATION," having Ellie Yieh, Li-Qun Xia, and Srinivas Nemani listed asco-inventors; and to concurrently filed and commonly assigned U.S.patent application Ser. No. 08/748,883 entitled "SYSTEMS AND METHODS FORHIGH TEMPERATURE PROCESSING OF SEMICONDUCTOR WAFERS," having VisweswarenSivaramakrishnan, Ellie Yieh, Jonathan Frankel, Li-Qun Xia, Gary Fong,Srinivas Nemani, Irwin Silvestre, Inna Shmurun, and Tim Levine listed asco-inventors; and to concurrently filed and commonly assigned U.S.patent application Ser. No. 08/746,658 entitled "METHODS AND APPARATUSFOR PRESTABILIZED PLASMA GENERATION FOR MICROWAVE CLEAN APPLICATIONS,"having Gary Fong, Fong Chang, and Long Nguyen listed as co-inventors;and to concurrently filed and commonly assigned U.S. patent applicationSer. No. 08/748,094 entitled "METHOD AND APPARATUS FOR FORMINGULTRA-SHALLOW DOPED REGIONS USING DOPED SILICON OXIDE FILMS," havingEllie Yieh, Li-Qun Xia, Paul Gee, and Bang Nguyen listed asco-inventors. Each of the above referenced applications are assigned toApplied Materials Inc., the assignee of the present invention, and eachof the above referenced applications are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

The present invention relates to semiconductor processing. Morespecifically, the invention relates to a method and apparatus forforming dielectric films over high aspect ratio features at temperaturesgreater than about 500° C., with the dielectric films having lowmoisture content and low shrinkage. Embodiments of the present inventionare particularly useful to deposit doped dielectric films, such asborophosphosilicate glass (BPSG) films, borosilicate glass (BSG) films,or phosphosilicate glass (PSG) films, and to form ultra-shallow dopedregions used, for example, as source/drain junctions or as channel stopdiffusions in shallow trench isolation. In addition, embodiments of thepresent invention may also be used to deposit doped dielectric filmsused as premetal dielectric (PMD) layers, intermetal dielectric (IMD)layers, or other dielectric layers. Further embodiments of the presentinvention may further be used to deposit undoped dielectric films, suchas undoped silicate glass (USG) films used as shallow trench isolationfilling oxides, insulating layers, capping layers, or other layers.

One of the primary steps in fabricating modern semiconductor devices isforming a dielectric layer on a semiconductor substrate. As is wellknown, such a dielectric layer can be deposited by chemical vapordeposition (CVD). In a conventional thermal CVD process, reactive gasesare supplied to the substrate surface where heat-induced chemicalreactions (homogeneous or heterogeneous) take place to produce a desiredfilm. In a conventional plasma process, a controlled plasma is formed todecompose and/or energize reactive species to produce the desired film.In general, reaction rates in thermal and plasma processes may becontrolled by controlling one or more of the following: temperature,pressure, and reactant gas flow rate.

Semiconductor device geometries have dramatically decreased in sizesince such devices were first introduced several decades ago. Sincethen, integrated circuits have generally followed the two-year/half-sizerule (often called "Moore's Law") which means that the number of deviceswhich will fit on a chip doubles every two years. Today's waferfabrication plants are routinely producing 0.5 μm and even 0.35 μmfeature size devices, and tomorrow's plants soon will be producingdevices having even smaller feature sizes. As device feature sizesbecome smaller and integration density increases, issues not previouslyconsidered crucial by the industry are becoming of greater concern. Inparticular, devices with increasingly high integration density havefeatures with high (for example, greater than about 3:1 or 4:1) aspectratios. (Aspect ratio is defined as the height-to-spacing ratio of twoadjacent steps.)

Increasingly stringent requirements for processes in fabricating thesehigh integration devices are needed in order to produce high qualitydevices, and conventional substrate processing systems are becominginadequate to meeting these requirements. One requirement is that thedielectric films formed in the process of fabricating such devices needto be uniformly deposited over these high aspect ratio features withoutleaving substantial gaps or voids. Another requirement is that thesefilms need to exhibit low shrinkage so that subsequent heating and/orwet etching steps do not cause voids to open up in the deposited film.However, conventional substrate processing systems that typicallydeposit dielectric films at temperatures less than about 450° C. areunable to produce low moisture films having good gap-fillingcapabilities without opening substantial voids in subsequent heatingand/or wet etching steps. As is well known, these gaps or voids maycontribute to device performance unreliability and other problems.Dielectric films used, for example, as PMD or IMD layers in such devicesneed good high aspect ratio gap-fill capability to avoid problems causedby these gaps or voids. A further requirement is that metalcontamination into the wafer during the processing steps be minimized toavoid short circuits and other problems in the devices. As is wellknown, conventional substrate processing systems using in situ plasmaduring processing experience physical sputtering of ions which attackchamber surfaces, such as aluminum walls, resulting in metalcontamination of the substrate. Use of in situ plasma is thereforeundesirable. An improved substrate processing system, which does not usein situ plasma, is needed to provide dielectric films with the desiredcharacteristics of low moisture, high density, low shrinkage, good highaspect ratio gap-filling capability.

In addition to meeting these stringent requirements, substrateprocessing systems must be able to meet the higher demands for formingultra-shallow doped regions, which are necessary for high integrationdevices with shrinking device geometries. With the advent of smallerdevice geometries, ultra-shallow doped regions in semiconductors areneeded for various applications including, for example, source/drainjunctions, channel stop diffusions for shallow trench isolation, etc.For example, MOS devices with channel lengths of less than 0.8 μm oftenrequire source/drain junctions having depths less than about 250nanometers (nm) for adequate device performance. For transistorsseparated by trench isolation structures of about 0.35 μm depth,ultra-shallow channel stop regions having a depth on the order ofhundreds of nm are usually required. For applications requiringultra-shallow doped regions, it is important to provide uniform dopantdistribution in the doped regions and good control of junction depth.

Current approaches to forming ultra-shallow doped regions, such as ionimplantation and gaseous diffusion, are inadequate in some applications.With these current approaches, the ability to control dopantdistribution and junction depth is limited, especially as the dopedregions become shallower. With an approach like ion implantation,controlling dopant distribution is made difficult due to the built-upconcentration of ions at the surface of the semiconductor material.Also, ion implantation causes damage to the semiconductor surface, andmethods for repairing this substrate damage often make it more difficultto control dopant distribution and junction depth for ultra-shallowdoped regions. For example, ions bombarded at relatively high energylevels have a tendency to tunnel or channel through the semiconductormaterial and cause damage such as point defects. These point defects,which may lead to irregular and nonuniform junction depths, may be fixedby annealing the implanted semiconductor material at high temperatures(greater than about 900° C.). Annealing the implanted semiconductormaterial, however, may further increase the junction depth beyond thatdesired. With an approach like gaseous diffusion, controlling dopantdistribution and junction depth is difficult to control in formingultra-shallow doped regions. As technology progresses to even smallergeometry devices, an alternative approach that is able to control thedopant uniformity and junction depth in ultra-shallow doped regions isneeded.

In forming ultra-shallow doped regions, one alternative approach to thecurrent approaches of ion implantation and gaseous diffusion is the useof a doped dielectric film as a dopant diffusion source. In thisalternative approach, a doped dielectric film is deposited onto asubstrate and used as a source of dopants which are diffused into thesubstrate to form ultra-shallow doped regions. For example, dopeddielectric films are deposited at temperatures less than 500° C. in adeposition chamber, and subsequently heated at temperatures greater than500° C. in a different chamber, such as an annealing furnace, to performthe dopant diffusion to form the doped region. Controlling thickness,uniformity, and moisture content of the doped dielectric film isimportant in efficiently forming ultra-shallow doped junctions in thesemiconductor material. Specifically, controlling the thickness anduniformity of the deposited doped dielectric film provides some controlover the amount of dopants available for diffusion. Limiting thethickness of doped dielectric films used as diffusion sources also helpsto increase wafer throughput by saving deposition (and subsequentetching) time. Moreover, a uniformly deposited film with even dopantuniformity can provide a more controlled diffusion of dopants from thefilm into the substrate. As is well known, moisture in doped dielectricfilms reacts with dopants to bind them in a crystal structure, resultingin fewer dopants available for diffusion into the substrate to formdoped regions. It is desirable to use doped dielectric films having alow moisture content, since these films have more dopants available foruse in the diffusion.

Several problems are encountered with conventional substrate processingsystems when using a doped dielectric film as a dopant diffusion source.One problem is that it is difficult to obtain a high degree of controlover film thickness and uniformity when using conventional systems todeposit the doped dielectric film. Another problem is that it is oftendifficult to ensure that adequate amounts of dopants in the dopeddielectric film are available for diffusion into the substrate to formthe ultra-shallow doped regions. A further problem is the existence ofnative oxides, which act as a barrier layer preventing dopants fromdiffusing into the substrate from the doped dielectric film, onsubstrate surfaces where the ultra-shallow doped regions are to beformed. These problems are discussed in further detail below.

Despite the advantages of using doped dielectric films as dopantdiffusion sources to form ultra-shallow doped regions, the problem ofbeing unable to control thickness and uniformity of the deposited dopeddielectric film when using conventional deposition systems is ofparticular concern for two primary reasons. First, the inability toadequately control thickness and uniformity of the deposited dopeddielectric film using conventional methods and apparatus undesirablyresults in a diminished ability to control the dopant uniformity andjunction depth of the ultra-shallow doped region formed. For example, ina conventional sequential CVD chamber, a substrate rests on a belt andtravels through various portions of the chamber. In each portion of thechamber, a layer having a certain thickness may be deposited. Thicknessof the deposited film may be controlled by changing the belt speed,which provides limited control. Further, control over the thickness anddopant uniformity of the films deposited on different wafers isdifficult when attempting to control film thickness and dopantconcentration using belt speed. That is, the thicknesses of thedeposited films on different wafers may vary and be unpredictable,leading to wafer-to-wafer unreliability. Second, being able to controlthe thickness of the deposited doped dielectric film, even for very thinfilms, is desirable for overall efficiency and increased waferthroughput. However, conventional approaches have only been capable offorming doped dielectric films with thicknesses on the order ofthousands of Angstroms (Å). Also, it may be difficult to maintain thethickness of the deposited film as thin as possible using systemsrelying on belt speed to control thickness of the deposited film. Withthicker films deposited conventionally, some dopants may take longer todiffuse into the substrate, since they have greater distances to travelbefore reaching the semiconductor material. Also, removal of such athick film used as a dopant diffusion source by etching or othertechnique often increases the total time to process the wafer. Withgrowing pressures on manufacturers to improve efficiency, it isdesirable to form the doped dielectric film as thin as possible in orderto decrease the time needed to deposit and then remove the film. It isdesirable to have a method and apparatus that can easily control thethickness and dopant uniformity of a doped dielectric film (less thanabout 500 Å thick at ±0.2 weight percentage dopant variation across thewafer) that is used as a dopant diffusion source.

Another problem with using doped dielectric films as dopant diffusionsources for ultra-shallow doped regions is that adequate amounts ofdopants must be available for diffusion into the substrate. Films withhigh dopant concentration are often needed to provide adequate amountsof dopants for uniform diffusion into the substrate to formultra-shallow junctions. However, moisture absorption and outgassing aretwo problems relating to adequate dopant availability. Doped dielectricfilms, especially those with high dopant concentrations, tend to absorbmoisture shortly after a wafer is exposed to ambient moisture in a cleanroom (e.g. when the wafer is transferred from the deposition chamberafter deposition of the doped dielectric film to a different processingchamber for the next processing step in a multiple-step process). Theabsorbed moisture (H₂ O) then reacts with the dopants in the dielectricfilm, causing the film to crystallize. Due to the crystal structurebinding the dopants within the film, these dopants become unavailablefor diffusion into the substrate, even after a subsequent heating of thewafer by rapid thermal processing or annealing in another chamber.Moisture absorption thus reduces the amount of dopants for diffusioninto the substrate. In addition to the moisture absorption problem,outgassing of dopants from the doped dielectric film also may occur insubsequent heating steps. These dopants diffuse out of the film awayfrom the substrate, resulting in fewer dopants available to be diffusedinto the substrate to form ultra-shallow doped regions.

Even if adequate dopants are available for diffusion, the problem ofnative oxides remains an important consideration when using dopeddielectric films as diffusion sources. Native oxides existing on thesubstrate surface where ultra-shallow doped regions are to be formedprevent effective and uniform dopant diffusion into the silicon.Therefore, native oxides, which act as a diffusion barrier layer to thedopants, need to be removed. Removing native oxides has been done usingconventional techniques such as wet etching using liquid etchants, anddry etching using an in situ plasma. However, using liquid etchants isoften difficult to control and may result in overetching the substrate.Substrates that have native oxides cleaned by conventional methods suchas wet etching have shelf lives of less than about one week beforenative oxides begin to form again, making it desirable to process thewafers shortly after the native oxides have been removed. Using dryetching to remove native oxides with an in situ plasma results in plasmadamage to the surface of the substrate. In addition to causing surfaceplasma damage, in situ plasma dry etching may undesirably result in moremetal contamination, as discussed earlier. Accordingly, it is importantto efficiently remove native oxides without damaging the substratesurface so dopants may diffuse into the substrate uniformly forultra-shallow doped regions.

In addition to providing dense, low moisture dielectric films havinguniform thickness and high aspect ratio gap-filling capability with lowmetal contamination, improved quality and overall efficiency infabricating integrated circuit devices is also important. An importantway to improve quality and overall efficiency in fabricating devices isto clean the chamber effectively and economically. With growingpressures on manufacturers to improve processing quality and overallefficiency, eliminating the total down-time in a multiple-step processwithout compromising the quality of the wafers has become increasinglyimportant for saving both time and money. During CVD processing,reactive gases released inside the processing chamber form layers suchas silicon oxides or nitrides on the surface of a substrate beingprocessed. Undesirable oxide deposition occurs elsewhere in the CVDapparatus, such as in the area between the gas mixing box and gasdistribution manifold. Undesired oxide residues also may be deposited inor around the exhaust channel and the walls of the processing chamberduring such CVD processes. Over time, failure to clean the residue fromthe CVD apparatus often results in degraded, unreliable processes anddefective substrates. Without frequent cleaning procedures, impuritiesfrom the residue built up in the CVD apparatus can migrate onto thesubstrate. The problem of impurities causing damage to the devices onthe substrate is of particular concern with today's increasingly smalldevice dimensions. Thus, CVD system maintenance is important for thesmooth operation of substrate processing, as well as resulting inimproved device yield and better product performance.

Frequently, periodic chamber cleanings between processing of every Nwafers is needed to improve CVD system performance in producing highquality devices. Providing an efficient, non-damaging clean of thechamber and/or substrate is often able to enhance performance andquality of the devices produced. In addition to improving the quality ofthe above-discussed chamber cleanings (which are done without breakingthe vacuum seal), preventive maintenance chamber cleanings (where thevacuum seal is broken by opening the chamber lid to physically wipe downthe chamber) are performed between multiple periodic chamber cleanings.Often, performing the necessary preventive maintenance chamber cleaningsinvolves opening the chamber lid and any other chamber parts that mightobstruct the lid, which is a time-consuming procedure that interfereswith normal production processing.

In light of the above, improved methods, systems and apparatus areneeded for depositing dense, low moisture dielectric films with uniformthicknesses and high aspect ratio gap-filling capabilities. Optimally,these improved methods and apparatus will also provide a chamber cleanwith low metal contamination. Improved methods and apparatus are alsoneeded for forming doped dielectric films as dopant diffusion sourcesfor ultra-shallow junctions. These methods and apparatus should becapable of efficiently removing native oxides to ensure effective anduniform dopant diffusion from the doped dielectric layer without causingsignificant surface damage to the silicon wafer. Further, for someapplications it is desirable to provide multiple deposition and cleaningcapabilities in a single chamber with a simplified design to minimizethe time consumed for different types of cleanings. What is needed,therefore, are systems and methods that are capable of high quality,efficient, high temperature deposition and efficient, gentle cleaning.In particular, these systems and methods should be designed to becompatible with processing requirements for forming devices with highaspect ratio features, and for forming ultra-shallow doped regions.

SUMMARY OF THE INVENTION

The present invention provides systems, methods and apparatus for hightemperature (at least about 500-800° C.) proessing of semiconductorwafers. Embodiments of the present invention include systems, methodsand apparatus which enable multiple process steps to be performed insitu in the same chamber to reduce total processing time and to ensurehigh quality processing to produce high integration devices having highaspect ratio features. Performing multiple process steps in the samechamber also increases the control over process parameters,substantially reduces moisture content in deposited films, and minimizesdevice damage due to metal contamination or process residuecontamination.

In particular, the present invention provides high temperaturedeposition, heating and efficient cleaning for forming dielectric filmshaving relatively thin film thicknesses. Embodiments of the presentinvention are particularly useful to deposit doped dielectric films,such as borophosphosilicate glass (BPSG) films, borosilicate glass (BSG)films, or phosphosilicate glass (PSG) films, and to form anultra-shallow doped region used, for example, as source/drain junctionsor as channel stop diffusions in shallow trench isolation. In addition,embodiments of the present invention may also be used to deposit dopeddielectric films used as premetal dielectric (PMD) layers, intermetaldielectric (IMD) layers, or other dielectric layers. Further embodimentsof the present invention may further be used to deposit undopeddielectric films used as shallow trench isolation filling oxides,insulating layers, capping layers, or other layers.

Methods according to the present invention include depositing dielectricfilms by CVD on a substrate in a vacuum chamber having a pressurebetween about 10-760 torr, and heating the substrate to a temperaturegreater than about 500° C. The substrate may be heated for a variety ofpurposes, such as performing reflow of deposited dielectric layers forplanarization, or for driving in dopants from a deposited dopeddielectric layer. The process may be carried out in a single step (e.g.,depositing and reflowing the film on the wafer at temperatures greaterthan 500° C.), or in multiple steps (e.g., depositing the film on thewafer at temperatures less than 500° C. and then heating the film on thewafer after the film has been deposited). In either case, hightemperature processing is accomplished without removing the wafer fromthe vacuum chamber, which advantageously reduces moisture absorption inthe dielectric film. The high temperature processing also enables insitu deposition of doped dielectric films with capping layers toadvantageously reduce outgassing of dopants from the doped film andlower moisture content. In a specific embodiment, reactive gases aredelivered to the substrate surface, where heat-induced chemicalreactions take place to produce the dielectric film. Additionally oralternatively, a controlled plasma may be formed to facilitate thedecomposition of the reactive species.

In an exemplary embodiment, the dielectric film is a thin doped filmused as a dopant diffusion source for an ultra-shallow junction. Thefilm is deposited at temperatures greater than about 500° C. onto thesubstrate and heated to higher temperatures, usually greater than 600°C. and preferably greater than about 700° C., to diffuse dopants fromthe dielectric layer to the underlying substrate. Performing thedeposition and heating steps in the same chamber provides better controlof the thickness, uniformity, and moisture content of the dopeddielectric film. Improving the moisture content of the film increasesthe amounts of available dopants in the film, which is particularlyadvantageous for forming ultra-shallow junctions in high integrationdevices.

In another aspect of the invention, a remote plasma system is providedfor etching undesired deposits on the inner walls of the vacuum chamberand components of the apparatus, and for cleaning native oxides andother residue from the semiconductor wafer prior to processing. A gentlecleaning technique using a remote energy source is preferably employedinstead of a conventional in situ plasma process to lower metalcontamination. For example, the remote plasma system provides a remoteplasma and preferably fluorine radicals from the plasma are able toenter the chamber, which is at high temperatures, and provide a gentle,thermal cleaning of the chamber. With the remote plasma system, onlychemical reactions are utilized and the problem of physical sputteringeffects are eliminated. In contrast, with the use of an in situ plasmasystem, sputtering effects attack aluminum chamber walls, which may thenlead to metal contamination in the processed wafer. In the thermalcleaning process using the remote plasma system, the radicals directedinto the chamber can effectively clean unwanted deposits and residuesfrom the surfaces in the chamber while the plasma remains remote orexterior to the chamber. Another advantage of the remote plasma systemis that native oxides can be efficiently removed from the wafer toeffectively ensure effective and uniform dopant diffusion from the dopeddielectric layer without causing significant surface damage to thesilicon wafer. A further advantage of the remote plasma system is thatthe system may also be configured for use to deposit films by usingdifferent input gases as needed.

In a preferred embodiment, the remote plasma cleaning system is amicrowave plasma system configured to produce and deliver a selectspecies (such as fluorine, chlorine or other radicals) to the processingchamber. The remote plasma system energizes gases by microwave radiationto create a plasma with etching radicals. Specifically, microwaves arecreated by a magnetron or other suitable energy source and directedthrough a waveguide system to an applicator tube, where a plasma iscreated. Reactive gases are then fed into the applicator tube andenergized by the microwave energy, which sustains the ionization of theignited plasma to produce a flow of radicals into the processingchamber. For cleaning, the radicals interact with residue formed on thechamber walls to form reactant gases that are suitably discharged formthe chamber by an exhaust system. The microwave plasma system may alsobe adapted to deposit plasma enhanced CVD films by delivering depositionreactive gases into the processing chamber.

In another aspect of the invention, the remote plasma system includes anendpoint detection system for indicating when the chamber cleaning hasconcluded. The lack of plasma in the chamber can make it difficult,using conventional endpoint detection systems, to pinpoint the time atwhich the cleaning has been completed (i.e., when the last process gasresidue in the chamber has reacted with the cleaning etchant so that itcan be discharged from the chamber). This is because conventionalendpoint detection systems typically rely on the use of a plasma withinthe chamber to check emissions from the in situ plasma to determine theend of the cleaning process. In the present invention, an endpointdetection assembly is coupled to the gas outlet of the processingchamber to determine the endpoint of the cleaning process by detectingchanges in light intensity that occur due to absorbance of light by theexhausted clean gas reactants, such as SiF₄.

In yet another aspect of the present invention, a method providesgettering of any adsorbed clean gases, such as fluorine, from thesurface of chamber walls. According to the present invention, a firstcleaning gas containing fluorine is introduced into the processingchamber to clean the processing chamber of deposition residue. A secondcleaning gas is then introduced into the processing chamber after theresidue has been removed with the first cleaning gas. The secondcleaning gas removes cleaning residue formed by the reaction between thefirst cleaning gas and the interior surfaces of the processing chamber.Removing or gettering the cleaning residue from the chamber provides anumber of advantages. For example, in a preferred embodiment of thepresent invention, fluorine radicals are delivered into the processingchamber to remove residue, such as silicon oxide, by forming asilicon-fluoride gas product which is pumped away from chamber. Afterthe fluorine-based chamber cleaning procedure, any adsorbed fluorine onthe surface of the chamber walls which might otherwise interact with, orbe incorporated into, the deposited film on the next wafer to beprocessed is gettered. In an alternative embodiment, the gettering maybe performed by seasoning the chamber using microwave-generated atomicoxygen and a silicon source to deposit a thin film of oxide onto thechamber to trap any adsorbed fluorine and prevent contamination of thesubsequently deposited films.

The present invention also provides various heat-resistant andprocess-compatible components for high temperature processing. Thesystem of the present invention includes a vapor deposition apparatushaving an enclosure assembly housing a processing chamber. The apparatusincludes a heating assembly having a pedestal/heater for heating thewafer to temperatures up to about 500-800° C. The pedestal preferablycomprises a material that is substantially resistant to reactions withthe process gases and to deposition by the process gases at temperaturesof at least about 400° C., and preferably at temperatures up to about500-800° C. In addition, the pedestal preferably comprises a materialthat is substantially resistant to etching at high temperatures (i.e.,500-800° C.) by the fluorine radicals introduced into the chamber duringcleaning. In an exemplary embodiment, the pedestal/heater comprises aresistive heating element imbedded in a ceramic material, such asaluminum oxide or preferably aluminum nitride.

The heating assembly of the present invention further includes a supportshaft for supporting the pedestal/heater within the chamber and forhousing the necessary electrical connections thereto. The support shaftpreferably comprises a ceramic material that is diffusion-bonded to thepedestal/heater to provide a vacuum seal within the shaft. This vacuumseal allows the hollow interior of the shaft to be maintained at ambienttemperature and pressure during high temperature processing, whichprotects the electrodes and other electrical connections from corrosionfrom the process and clean gases within the chamber. In addition,providing ambient pressure within the shaft minimizes arcing from thepower source through the hollow core of the shaft to power leads or theouter walls of the shaft.

In still another aspect of the invention, a chamber liner is providedaround the pedestal/heater to insulate the chamber walls from theheater. Preferably, the chamber liner includes an inner portioncomprised of a material such as ceramic that is resistant to hightemperatures and to deposition/clean reactions, and an outer portioncomprised of a material resistant to cracking. The inner portion of theliner insulates the chamber walls to reduce the wafer edge coolingeffects which might otherwise adversely affect deposited filmuniformity. The outer portion of the chamber liner is substantiallythicker than the inner portion to bridge the gap between the wafer andthe walls, while minimizing cracking which might otherwise occur with asingle, relatively thick ceramic liner. In an exemplary embodiment, theouter portion of the liner includes air gaps to increase the insulationprovided by the liner.

In still a further aspect of the invention, a lid assembly is providedfor the enclosure assembly. The lid assembly includes a gas mixing block(or box) coupled to one or more clean gas passages and one or moreprocess gas passages for receiving process and clean gases and fordelivering these gases into the chamber. One or more valves are providedon either the clean gas passages or the process gas passages toselectively allow gas to flow through to the gas mixing block. Thisembodiment facilitates the in situ cleaning method of the presentinvention by allowing the apparatus to quickly and efficiently switchbetween processing and cleaning, which increases the throughput of thesystem.

In an exemplary embodiment, the lid assembly further includes a baseplate having a gas inlet for receiving one or more gases and a gasdistribution plate including a plurality of holes for dispersing thegases into the processing chamber. The lid assembly includes one or morebypass passages in the base plate that offer less resistance to fluidflow than the gas distribution holes. During cleaning, for example, atleast a portion of the cleaning gases will pass through the bypasspassages directly into the chamber to increase the speed of the cleaningprocess, thereby decreasing the down time of the chamber. The apparatuspreferably includes a control system, such as a valve and a controller,for partially or completely closing the bypass passages to control thegas flow through the gas distribution holes.

These and other embodiments of the present invention, as well as itsadvantages and features, are described in more detail in conjunctionwith the text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a vertical, cross-sectional view of a CVD apparatus accordingto the present invention;

FIG. 1B is a simplified diagram of the system monitor and CVD apparatus10 in a multichamber system;

FIG. 1C illustrates a general overview of CVD apparatus 10 in relationto a gas supply panel 80 located in a clean room;

FIG. 1D is an illustrative block diagram of the hierarchical controlstructure of the system control software, computer program 150,according to a specific embodiment;

FIG. 1E is a block diagram of an exemplary heater control subroutine;

FIG. 2 is an exploded view of a preferred embodiment of CVD apparatus 10according to the present invention;

FIG. 3 is a vertical cross-section, partly in schematic, taken alongline 3--3 in FIG. 2;

FIG. 4 is an enlarged cross-section of a semiconductor processingchamber of the apparatus of FIG. 2;

FIG. 5 is an exploded view of a gas distribution system for theapparatus of FIG. 2;

FIG. 6A is a top, partially cut-away view of a lid assembly of CVDapparatus 10, illustrating portions of the gas distribution systems;

FIGS. 6B and 6C illustrate a front cross-section and a top view,respectively, of an alternative lid assembly for CVD apparatus 10,incorporating a bypass conduit for cleaning gases;

FIGS. 7A and 7B are side cross-sectional views and bottom views,respectively, of a chamber liner, in accordance with an embodiment ofthe invention;

FIG. 8 is a partially schematic, cross-sectional view of FIG. 3 takenalong lines 8--8, illustrating the pumping channel and the gas flowpattern in the exhaust system of the CVD apparatus 10 of FIG. 2;

FIG. 9 is a vertical cross-sectional view, partially schematic, of aheater/lift assembly, according to an embodiment of the invention;

FIG. 10 is an enlarged cross-sectional view of a bottom portion of theheater/lift assembly of FIG. 9;

FIG. 11 is a side cross-sectional view of a pedestal/heater of theassembly of FIG. 9, according to an embodiment of the invention;

FIG. 12 is a bottom view of the pedestal/heater, illustrating a heatercoil;

FIG. 13 is an exploded view of the heater/lift assembly of FIG. 9;

FIG. 14 is an enlarged view of one of the electrical connections withinthe pedestal/heater of FIG. 10;

FIGS. 15A and 15B illustrate a hole within the pedestal/heater forreceiving a thermocouple and the thermocouple, respectively;

FIG. 16 is a simplified diagram of a remote microwave plasma system forcleaning the wafer and/or the process chamber, in accordance with anembodiment of the present invention;

FIGS. 17A-17D are schematic diagrams of a cleaning endpoint detectionsystem in accordance with an embodiment of the present invention;

FIG. 18 is a simplified cross-sectional view of a semiconductor devicemanufactured according to an embodiment of the present invention;

FIGS. 19A-19E are simplified cross-sectional views of an exemplaryapplication of the method and apparatus of the present invention for anultra-shallow source/drain junction;

FIGS. 20A-20G are simplified cross-sectional views of another exemplaryapplication of the method and apparatus of the present invention forultra-shallow trench isolation;

FIG. 21 illustrates the relationship between NF₃ flow and microwavesaturation power that gives optimal cleaning rates provided with remotemicrowave plasma system 55 in accordance with a specific embodiment ofthe present invention;

FIGS. 22A-22C are graphs illustrating experimental results showing thedopant profile of the ultra-shallow junctions formed using capped BSGfilms produced according to an embodiment of the present invention;

FIGS. 23A-23F are graphs illustrating further experimental resultsshowing the dopant profile and sheet resistivity of the ultra-shallowjunctions formed using different capped BSG films according to anotherembodiment of the present invention;

FIG. 24A is a photomicrograph demonstrating the as-deposited gap fillcapabilities of PSG films deposited at 600° C. in accordance with aspecific embodiment of the present invention;

FIG. 24B is a simplified diagram of a section of the structure shown inFIG. 24A;

FIG. 25 illustrates the FTIR spectra of a PSG film deposited at about600° C. under exemplary process conditions, according to a specificembodiment;

FIGS. 26A and 26B are photomicrographs demonstrating the relative gapfill capabilities of TEOS/O₃ USG films deposited at about 400° C. andabout 550° C., respectively, after heating at about 1050° C. and asubsequent wet etch processing, in accordance with a specific embodimentof the present invention;

FIG. 27 is a photomicrograph demonstrating the gap fill capability of aUSG film deposited at about 550° C. after heating at about 1000° C. anda subsequent wet etch processing, in accordance with a specificembodiment of the present invention; and

FIG. 28 illustrates the FTIR spectra of a USG film deposited at about550° C. under exemplary process conditions, according to a specificembodiment.

DETAILED DESCRIPTION OF THE SPECIFIC EMBODIMENTS I. CVD Reactor System

A. Overview of CVD Reactor

Embodiments of the present invention are systems, methods and apparatusused for depositing dielectric films at temperatures greater than about500° C. In particular, such systems, methods and apparatus may be usedto deposit undoped dielectric films and doped dielectric films. Suchfilms may be used to form ultra-shallow doped regions, premetaldielectric layers, intermetal dielectric layers, capping layers, oxidefilling layers, or other layers. FIG. 1A is a vertical, cross-sectionalview of one embodiment of a CVD apparatus 10 according to a specificembodiment. In addition to being capable of depositing dielectriclayers, the apparatus according to the present invention has hightemperature heating capabilities useful for performing reflow ofdeposited dielectric layers for planarization, or for driving in dopantsfrom a deposited doped dielectric layer when forming ultra-shallow dopedregions. Further, the apparatus can provide efficient cleaning ofvarious CVD chamber components and cleaning of wafer surfaces. CVDapparatus 10 provides these multiple capabilities in situ in a singlevacuum chamber 15. Accordingly, multiple process steps may be performedin a single chamber without having the wafer transferred out of thatchamber into other external chambers. This results in a lower moisturecontent on the wafers by eliminating opportunities to absorb moisturefrom the ambient air and, advantageously increases the dopant retentionin the deposited dielectric layer. In addition, performing multipleprocess steps in a single chamber saves time, which increases theoverall throughput of the process.

Referring to FIG. 1A, CVD apparatus 10 includes an enclosure assembly200 housing a vacuum chamber 15 with a gas reaction area 16. A gasdistribution plate 20 is provided above the gas reaction area 16 fordispersing reactive gases through perforated holes in plate 20 to awafer (not shown) that rests on a vertically movable heater 25 (alsoreferred to as a wafer support pedestal or susceptor). CVD apparatus 10further includes a heater/lift assembly 30 for heating the wafersupported on heater 25. Heater/lift assembly 30 also can be controllablymoved between a lower loading/off-loading position and an upperprocessing position indicated by dotted line 13 which is closelyadjacent to plate 20, as shown in FIG. 1A. A center board (not shown)includes sensors for providing information on the position of the wafer.As discussed in detail below, heater 25 includes resistively-heatedcomponents enclosed in a ceramic, preferably aluminum nitride. In anexemplary embodiment, all surfaces of heater 25 exposed to vacuumchamber 15 are made of a ceramic material, such as aluminum oxide (Al₂O₃ or alumina) or aluminum nitride. When heater 25 and the wafer are inprocessing position 13, they are surrounded by a chamber liner 35 alongthe inside walls 17 of apparatus 10 and by an annular pumping channel40, formed by chamber liner 35 and a top portion of chamber 15. Asdiscussed in detail below, the surface of chamber liner 35 preferablycomprises a ceramic material, such as alumina or aluminum nitride, whichserves to lower the temperature gradient between resistively-heatedheater 25 (high temperature) and chamber walls 17, which are at a muchlower temperature relative to heater 25.

Reactive and carrier gases are supplied through supply line 43 into agas mixing box (or gas mixing block) 273 (FIG. 5), where they arepreferably mixed together and delivered to plate 20. Gas mixing box 273is preferably a dual input mixing block coupled to a process gas supplyline 43 and to a cleaning gas conduit 47. As will be discussed in detailbelow, a processor 50 preferably controllably operates a gate valve 280(FIG. 5) to choose which of these two alternate sources of gases aresent to plate 20 for dispersing into chamber 15. Conduit 47 receivesgases from an integral remote microwave plasma system 55, which has aninlet 57 for receiving input gases. During deposition processing, gassupplied to plate 20 is vented toward the wafer surface (as indicated byarrows 21), where it may be uniformly distributed radially across thewafer surface, typically in a laminar flow. Purging gas may be deliveredinto chamber 15 from an inlet port or tube (not shown) through thebottom wall of enclosure assembly 200. The purging gas flows upward pastheater 25 and to an annular pumping channel 40. An exhaust system thenexhausts the gas (as indicated by arrows 22) into the annular pumpingchannel 40 and through an exhaust line 60 by a vacuum pump system (notshown). Exhaust gases and residues are preferably released from annularpumping channel 40 through exhaust line 60 at a rate controlled by athrottle valve system 63.

In the representative embodiment, the chemical vapor deposition processperformed in CVD apparatus 10 is a thermal, sub-atmospheric pressureprocess, often referred to as sub-atmospheric CVD (SACVD). As discussedearlier, thermal CVD processes supply reactive gases to the substratesurface where heat-induced chemical reactions (homogeneous orheterogeneous) take place to produce a desired film. In CVD apparatus10, heat is distributed by resistively-heated heater 25, as discussed indetail below, that is capable of reaching temperatures as high as about400-800° C. Such heat distribution provides uniform, rapid thermalheating of the wafer for effecting deposition, reflow and/or drive-in,cleaning, and/or seasoning/gettering steps in a multiple-step process insitu in chamber 15. Alternatively, a controlled plasma may be formedadjacent to the wafer by RF energy applied to gas distribution plate 20from an RF power supply (not shown). In embodiments additionally havinga lower RF electrode, the RF power supply can supply either singlefrequency RF power to plate 20 or mixed frequency RF power to plate 20and the lower RF electrode to enhance the decomposition of reactivespecies introduced into process chamber 15. In a plasma process, some ofthe components of vapor deposition apparatus 10 would have to bemodified to accommodate the RF energy, as discussed below.

Remote microwave plasma system 55 integrally provided in CVD apparatus10 is preferably adapted for performing periodic cleaning of undesireddeposition residue from various components of chamber 15, includingwalls 17 as well as other components. Further, remote microwave plasmasystem 55 can also perform cleaning or etching of native oxides orresidues from the surface of the wafer, depending on the desiredapplication. Although gases input via line 57 into plasma system 55 arereactive cleaning gases for creating a plasma to provide fluorine,chlorine, or other radicals, remote microwave plasma system 55 also maybe adapted to deposit plasma enhanced CVD films by inputting depositionreactive gases into system 55 via input line 57. Generally, remotemicrowave plasma system 55 receives gases via input line 57, which areenergized by microwave radiation to create a plasma with etchingradicals which are then sent via conduit 47 for dispersion through plate20 to chamber 15. Specific details of plasma system 55 will be discussedfurther below. Some embodiments of apparatus 10 may also include a radiofrequency (RF) plasma system to provide in situ plasma capability.

Motors and optical sensors (not shown) are used to move and determinethe position of movable mechanical assemblies such as throttle valvesystem 63 and heater 25. The heater/lift assembly 30, motors, gate valve280, throttle valve system 63, remote microwave plasma system 55, andother system components are controlled by processor 50 over controllines 65, of which only some are shown.

Processor 50 controls all of the activities of the CVD machine. Actingas the system controller, processor 50 executes system control software,which is a computer program stored in a memory 70 coupled to processor50. Preferably, memory 70 may be a hard disk drive, but of course memory70 may be other kinds of memory. In addition to a hard disk drive (e.g.,memory 70), CVD apparatus 10 in a preferred embodiment includes a floppydisk drive and a card rack. Processor 50 operates under the control ofthe system control software, which includes sets of instructions thatdictate the timing, mixture of gases, chamber pressure, chambertemperature, microwave power levels, susceptor position, and otherparameters of a particular process. Other computer programs such asthose stored on other memory including, for example, a floppy disk orother computer program product inserted in a disk drive or otherappropriate drive, may also be used to operate processor 50. Systemcontrol software will be discussed in detail below. The card rackcontains a single-board computer, analog and digital input/outputboards, interface boards and stepper motor controller boards. Variousparts of CVD apparatus 10 conform to the Versa Modular European (VME)standard which defines board, card cage, and connector dimensions andtypes. The VME standard also defines the bus structure having a 16-bitdata bus and 24-bit address bus.

The interface between a user and processor 50 is via a CRT monitor 73aand light pen 73b, shown in FIG. 1B which is a simplified diagram of thesystem monitor and CVD apparatus 10, illustrated as one of the chambersin a multichamber system. CVD apparatus 10 is preferably attached to amainframe unit 75 which contains and provides electrical, plumbing andother support functions for the apparatus 10. Exemplary mainframe unitscompatible with the illustrative embodiment of CVD apparatus 10 arecurrently commercially available as the Precision 5000™ and the Centura5200™ systems from Applied Materials, Inc. of Santa Clara, Calif. Themultichamber system has the capability to transfer a wafer between itschambers without breaking the vacuum and without having to expose thewafer to moisture or other contaminants outside the multichamber system.An advantage of the multichamber system is that different chambers inthe multichamber system may be used for different purposes in the entireprocess. For example, one chamber may be used for deposition of oxides,another may be used for rapid thermal processing, and yet another may beused for oxide cleaning. The process may proceed uninterrupted withinthe multichamber system, thereby preventing contamination of wafers thatoften occurs when transferring wafers between various separateindividual chambers (not in a multichamber system) for different partsof a process.

In the preferred embodiment two monitors 73a are used, one mounted inthe clean room wall for the operators and the other behind the wall forthe service technicians. Both monitors 73a simultaneously display thesame information, but only one light pen 73b is enabled. The light pen73b detects light emitted by CRT display with a light sensor in the tipof the pen. To select a particular screen or function, the operatortouches a designated area of the display screen and pushes the button onthe pen 73b. The touched area changes its highlighted color, or a newmenu or screen is displayed, confirming communication between the lightpen and the display screen. Of course, other devices, such as akeyboard, mouse, or other pointing or communication device, may be usedinstead of or in addition to light pen 73b to allow the user tocommunicate with processor 50.

FIG. 1C illustrates a general overview of CVD apparatus 10 in relationto a gas supply panel 80 located in a clean room. As discussed above,CVD apparatus 10 includes chamber 15 with heater 25, gas mixing box 273with inputs from supply line 43 and conduit 47, and remote microwaveplasma system 55 with input line 57. As mentioned above, gas mixing box273 is for mixing and injecting deposition gas(es) and clean gas(es) orother gas(es) through inlet tube 43 to the processing chamber 15. Asseen in FIG. 1C, remote microwave plasma system 55 is integrally locatedand mounted below chamber 15 with conduit 47 coming up alongside chamber15 to gate valve 280 and gas mixing box 273, located above chamber 15.Similarly, gas supply line 43, which comes up alongside chamber 15 togas mixing box 273, is provided with reactive gases via lines 83 and 85from gas supply panel 80. Gas supply panel 80 includes lines to gas orliquid supply sources 90, containing gases or liquids that may varydepending on the desired processes used for a particular application.Gas supply panel 80 has a mixing system 93 which receives the depositionprocess and carrier gases (or vaporized liquids) from sources 90 formixing and sending to gas mixing box 273 via line 85 to supply line 43.Generally, supply lines for each of the process gases include (i)shut-off valves 95 that can be used to automatically or manually shutoff the flow of process gas into line 85 or line 57, and (ii) mass flowcontrollers 100 that measure the flow of gas or liquid through thesupply lines. When toxic gases (for example, ozone and the clean gas)are used in the process, the several shut-off valves 95 may bepositioned on each gas supply line in conventional configurations. Therate at which the deposition and carrier gases including, for example,tetraethylorthosilane (TEOS), helium (He), and nitrogen (N₂), andoptionally triethylphosphate (TEPO), triethylborate (TEB), and/or otherdopant sources, are supplied to gas mixing system 93 is also controlledby liquid or gas mass flow controllers (MFCs) (not shown) and/or byvalves (not shown). In some embodiments, gas mixing system 93 includes aliquid injection system for vaporizing reactant liquids such as TEOS andTEPO. According to these embodiments, a mixture including TEPO as thephosphorus source, TEOS as the silicon source, and one or more gaseousoxygen sources, such as oxygen (O₂) or ozone (O₃), may be formed withgas mixing system 93. The TEPO and TEOS are all liquid sources that alsomay be vaporized by conventional boiler-type or bubbler-type hot boxesin other embodiments. A liquid injection system is preferred as itprovides greater control of the volume of reactant liquid introducedinto the gas mixing system. The vaporized gases are then mixed in thegas mixing system with a carrier gas, such as helium, before beingdelivered to heated line 85. Of course, it is recognized that othersources of dopants, silicon, and oxygen also may be used.

Additionally, gas supply panel 80 includes switching valve 95, whichunder the control of processor 50, can selectively send the clean gaswith N₂ along process gas line 83 to gas supply line 43 or along cleangas line 57 to remote microwave plasma system 55. When processor 50causes switching valve 95 to send the clean gas with N₂ via input line57 to plasma system 55, a plasma remote from chamber 15 is formed due toapplication of microwave energy and cleaning radicals are produced fortransfer to gas conduit 47. Processor 50 can also cause another valve 96to send ozone through line 83 to gas supply line 43 and to send thedeposition and carrier gases from gas mixing system 93 through heatedline 85 to gas supply line 43. In alternative embodiments, valve 95 isconnected at its output only to line 97 and selectively allows clean gasand N₂ to pass through line 97 to a switching valve 105 (not shown).Located at a point close to inlet 57 and remote system 55, switchingvalve 105 in these embodiments would be connected to inlet 57 to remotemicrowave system 55 and also to line 83 leading to inlet 43. In specificembodiments, gate valve 280 may be controlled by processor 50, withinstructions from the system software computer program, to select eitherthe clean gases or the deposition gases to flow into chamber 15.

Located remote from the clean room where chamber 15 of apparatus 10 islocated are a microwave power supply 110 and ozonator 115. Power supply110 provides power to the magnetron in remote plasma system 55. Ozonator115, applies power to oxygen (O₂) which is used as input to provideozone (O₃) as output for use as at least one of the sources 90. In otherembodiments, power supply 110 and ozonator 115 may be located in theclean room rather than being remotely located. Further, in multichambersystems requiring multiple ozone sources and/or multiple remotemicrowave plasma systems 55, multiple ozonators 115 and multiple powersupplies 110 may be provided.

The processes for depositing the film, performing a clean, andperforming reflow or drive-in steps can be implemented using a computerprogram product that is executed by processor 50. The computer programcode can be written in any conventional computer readable programminglanguage such as, for example, 68000 assembly language, C, C++, Pascal,Fortran, or other language. Suitable program code is entered into asingle file, or multiple files, using a conventional text editor and isstored or embodied in a computer-usable medium, such as a memory systemof the computer. If the entered code text is in a high-level language,the code is compiled, and the resultant compiler code is then linkedwith an object code of precompiled Windows library routines. To executethe linked compiled object code, the system user invokes the objectcode, causing the computer system to load the code in memory, from whichthe CPU reads and executes the code to perform the tasks identified inthe program.

FIG. 1D is an illustrative block diagram of the hierarchical controlstructure of the system control software, computer program 150,according to a specific embodiment. Using a light pen interface, a userenters a process set number and process chamber number into a processselector subroutine 153 in response to menus or screens displayed on theCRT monitor. The process sets, which are predetermined sets of processparameters necessary to carry out specified processes, are identified bypredefined set numbers. Process selector subroutine 153 identifies (i)the desired process chamber, and (ii) the desired set of processparameters needed to operate the process chamber for performing thedesired process. The process parameters for performing a specificprocess relate to process conditions such as, for example, process gascomposition and flow rates, temperature, pressure, plasma conditionssuch as magnetron power levels (and alternatively to or in addition tohigh- and low-frequency RF power levels and the low-frequency RFfrequency, for embodiments equipped with RF plasma systems), cooling gaspressure, and chamber wall temperature. Process selector subroutine 153controls what type of process (deposition, wafer cleaning, chambercleaning, chamber gettering, reflowing) is performed at a certain timein chamber 15. In some embodiments, there may be more than one processselector subroutine. The process parameters are provided to the user inthe form of a recipe and may be entered utilizing the light pen/CRTmonitor interface.

The signals for monitoring the process are provided by the analog inputboard and digital input board of the system controller, and the signalsfor controlling the process are output on the analog output board anddigital output board of CVD system 10.

A process sequencer subroutine 155 comprises program code for acceptingthe identified process chamber and set of process parameters fromprocess selector subroutine 153, and for controlling operation of thevarious process chambers. Multiple users can enter process set numbersand process chamber numbers, or a single user can enter multiple processset numbers and process chamber numbers, so sequencer subroutine 155operates to schedule the selected processes in the desired sequence.Preferably, sequencer subroutine 155 includes program code to performthe steps of (i) monitoring the operation of the process chambers todetermine if the chambers are being used, (ii) determining whatprocesses are being carried out in the chambers being used, and (iii)executing the desired process based on availability of a process chamberand the type of process to be carried out. Conventional methods ofmonitoring the process chambers can be used, such as polling. Whenscheduling which process is to be executed, sequencer subroutine 155 canbe designed to take into consideration the present condition of theprocess chamber being used in comparison with the desired processconditions for a selected process, or the "age" of each particularuser-entered request, or any other relevant factor a system programmerdesires to include for determining scheduling priorities.

Once sequencer subroutine 155 determines which process chamber andprocess set combination is going to be executed next, the sequencersubroutine 155 initiates execution of the process set by passing theparticular process set parameters to a chamber manager subroutine 157a-cwhich controls multiple processing tasks in a process chamber 15according to the process set determined by sequencer subroutine 155. Forexample, the chamber manager subroutine 157a comprises program code forcontrolling CVD and cleaning process operations in process chamber 15.Chamber manager subroutine 157 also controls execution of variouschamber component subroutines which control operation of the chambercomponents necessary to carry out the selected process set. Examples ofchamber component subroutines are substrate positioning subroutine 160,process gas control subroutine 163, pressure control subroutine 165,heater control subroutine 167, plasma control subroutine 170, endpointdetect control subroutine 159, and gettering control subroutine 169.Depending on the specific configuration of the CVD chamber, someembodiments include all of the above subroutines, while otherembodiments may include only some of the subroutines. Those havingordinary skill in the art would readily recognize that other chambercontrol subroutines can be included depending on what processes are tobe performed in process chamber 15. In operation, chamber managersubroutine 157a selectively schedules or calls the process componentsubroutines in accordance with the particular process set beingexecuted. Chamber manager subroutine 157a schedules the processcomponent subroutines much like sequencer subroutine 155 schedules whichprocess chamber 15 and process set are to be executed next. Typically,chamber manager subroutine 157a includes steps of monitoring the variouschamber components, determining which components need to be operatedbased on the process parameters for the process set to be executed, andinitiating execution of a chamber component subroutine responsive to themonitoring and determining steps.

Operation of particular chamber component subroutines will now bedescribed with reference to FIG. 1D. Substrate positioning subroutine160 comprises program code for controlling chamber components that areused to load the substrate onto heater 25 and, optionally, to lift thesubstrate to a desired height in chamber 15 to control the spacingbetween the substrate and gas distribution manifold 20. When a substrateis loaded into process chamber 15, heater 25 is lowered to receive thesubstrate and then heater 25 is raised to the desired height. Inoperation, substrate positioning subroutine 160 controls movement ofheater 25 in response to process set parameters related to the supportheight that are transferred from chamber manager subroutine 157a.

Process gas control subroutine 163 has program code for controllingprocess gas composition and flow rates. Process gas control subroutine163 controls the open/close position of the safety shut-off valves, andalso ramps up/down the mass flow controllers to obtain the desired gasflow rate. Process gas control subroutine 163 is invoked by the chambermanager subroutine 157a, as are all chamber component subroutines, andreceives subroutine process parameters related to the desired gas flowrates from the chamber manager. Typically, process gas controlsubroutine 163 operates by opening the gas supply lines and repeatedly(i) reading the necessary mass flow controllers, (ii) comparing thereadings to the desired flow rates received from chamber managersubroutine 157a, and (iii) adjusting the flow rates of the gas supplylines as necessary. Furthermore, process gas control subroutine 163includes steps for monitoring the gas flow rates for unsafe rates, andactivating the safety shut-off valves when an unsafe condition isdetected. Process gas control subroutine 163 also controls the gascomposition and flow rates for clean gases as well as for depositiongases, depending on the desired process (clean or deposition or other)that is selected. Alternative embodiments could have more than oneprocess gas control subroutine 613, each subroutine 613 controlling aspecific type of process or specific sets of gas lines.

In some processes, an inert gas such as nitrogen or argon is flowed intochamber 15 to stabilize the pressure in the chamber before reactiveprocess gases are introduced. For these processes, process gas controlsubroutine 163 is programmed to include steps for flowing the inert gasinto chamber 15 for an amount of time necessary to stabilize thepressure in the chamber, and then the steps described above would becarried out. Additionally, when a process gas is to be vaporized from aliquid precursor, for example TEOS, process gas control subroutine 163would be written to include steps for bubbling a delivery gas such ashelium through the liquid precursor in a bubbler assembly, orintroducing a carrier gas such as helium to a liquid injection system.When a bubbler is used for this type of process, process gas controlsubroutine 163 regulates the flow of the delivery gas, the pressure inthe bubbler, and the bubbler temperature in order to obtain the desiredprocess gas flow rates. As discussed above, the desired process gas flowrates are transferred to process gas control subroutine 163 as processparameters. Furthermore, process gas control subroutine 163 includessteps for obtaining the necessary delivery gas flow rate, bubblerpressure, and bubbler temperature for the desired process gas flow rateby accessing a stored table containing the necessary values for a givenprocess gas flow rate. Once the necessary values are obtained, thedelivery gas flow rate, bubbler pressure and bubbler temperature aremonitored, compared to the necessary values and adjusted accordingly.

The pressure control subroutine 165 comprises program code forcontrolling the pressure in the chamber 15 by regulating the aperturesize of the throttle valve in the exhaust system of the chamber. Theaperture size of the throttle valve is set to control the chamberpressure at a desired level in relation to the total process gas flow,the size of the process chamber, and the pumping set-point pressure forthe exhaust system. When pressure control subroutine 165 is invoked, thedesired or target pressure level is received as a parameter from chambermanager subroutine 157a. The pressure control subroutine 165 measuresthe pressure in chamber 15 by reading one or more conventional pressurenanometers connected to the chamber, compares the measure value(s) tothe target pressure, obtains PID (proportional, integral, anddifferential) values corresponding to the target pressure from a storedpressure table, and adjusts the throttle valve according to the PIDvalues obtained from the pressure table. Alternatively, pressure controlsubroutine 165 can be written to open or close the throttle valve to aparticular aperture size to regulate the pressure in chamber 15 to thedesired level.

Heater control subroutine 167 comprises program code for controlling thetemperature of a heater element 473 used to resistively heat heater 25(and any substrate thereon). Referring to FIG. 1E, heater controlsubroutine 167, which is also invoked by chamber manager subroutine157a, receives a desired target/set-point temperature parameter,T_(des), as an input (step 580). In step 582, heater control subroutine167 measures the current temperature of heater 25 by measuring voltageoutput of a thermocouple located in heater 25. The current temperatureis denoted T(k), where k is the current time step of heater controlsubroutine 167. The controller obtains the temperature T(k) from thethermocouple voltage by looking up the corresponding temperature in astored conversion table or by calculating the temperature using afourth-order polynomial. In an exemplary embodiment, heater controlsubroutine 167 in step 584 calculates the temperature error. Thetemperature error, denoted Err_(temp), is determined by the equationErr_(temp) (k)=T_(des) -T(k).

In step 584, heater control subroutine 167 will select one of twocontrol algorithms based on the absolute value of Err_(temp) (k). If theabsolute value of the temperature error is smaller than a predeterminedboundary error, the heater control subroutine will select a temperatureregulator algorithm (steps 586 and 588). This algorithm preciselycontrols the temperature at the desired temperature, T_(des). If theabsolute value of the temperature error is greater than the boundaryerror, heater control subroutine 167 will select a temperature rampcontrol algorithm (step 590). This algorithm controls the rate at whichthe heater temperature will approach the desired temperature, T_(des),it controls the rate at which the temperature changes.

The temperature regulator algorithm (steps 586 and 588) uses feedbackand feedforward control to update the power delivered to the heatingelement embedded in heater 25 so as to maintain the current temperature,T(k), as close to T_(des) as possible. The feedforward control in thisalgorithm estimates the amount of power necessary to maintain thedesired temperature given the amount and type of gas flow and RF powersupplied to the chamber. The feedback control uses standardProportional-Integral-Derivative (PID) control terms to adjust theestimated feedforward power based on the dynamic behavior of thetemperature error, Err_(temp) (k). PID control is the type of algorithmused in conventional heater control systems without regard to the valueof the temperature error. If these routines seek to control thetemperature ramp rate, they will define a time-varying T_(des) (k) andthen employ the PID controller described above to track this desiredtemperature trajectory.

In the present invention, heater control subroutine 167 preferablyemploys the temperature ramp control algorithm (steps 590) to controlpower to heater 25 when the absolute value of temperature error isgreater than the boundary error. This algorithm controls T'(k), which isthe rate of change of the temperature, T(k), at time step k. The rate ofchange of temperature should be controlled because the heater 25 can bemade of a ceramic material, which may fracture from thermal shock if thetemperature changes too quickly. The ramp control algorithm usesfeedforward and Proportional feedback control to control T'(k) to apredetermined desired ramp rate function, T'_(des) (T). The desired ramprate is mainly a function of the temperature of the heater and is basedon the thermal shock resistance of the heater 25 at varioustemperatures. Thus, the desired ramp rate may continuously change basedon the current measured temperature of the heater, or it may be set at aconstant based on a minimum rate that is low enough to avoid thermalshock within the range of temperatures of a particular process. Thecontrol algorithm also employs a saturation function on the rate ofchange of power supplied to the heater to damp the system response,which reduces oscillations in ramp rate.

Controllers that attempt to regulate ramp rate by tracking a timedtemperature trajectory at best can only guarantee that a desiredtemperature, T_(des) (K), will be achieved at some time K in the future.The average ramp rate over the time interval of length K will beT'_(des). However, the instantaneous rate of change of temperature T'(k)may vary widely during that interval. Consider the case in which adisturbance causes the temperature to remain stable for some interval oftime less than K. The controller will then attempt to as quickly aspossible "catch up" to the desired trajectory T_(des) (k). The ramp ratefor the time interval during which the controller is catching up will begreater than T'_(des). That scenario could result in thermal shockfracture. By controlling the ramp rate directly, the current inventionavoids this potential scenario.

Referring to FIG. 1E, an exemplary ramp control algorithm will now bedescribed. After the desired temperature, T_(des) is input (step 580),the current temperature T(k) is measured (step 582), and the temperatureerror is determined (step 584), the ramp control algorithm calculatesthe actual ramp rate T'(k) using a numerical differentiation technique.It also determines the desired ramp rate, T'_(des) (T(k)), based on thecurrent value of T(k), and the error in ramp rate, Err_(rrate) =T'_(des)(T(k))-T'(k) (steps 592 and 594). The actual ramp rate T'(k) iscalculated from measured temperature T(k) over a range of temperaturemeasurement samples. In general, T'_(des) (T(k)) may be any continuousfunction of temperature in various embodiments. In the specificembodiment, T'_(des) (T(k)) is set to be a predetermined constant value.The calculated ramp rate T'(k) is determined by sampling (i.e.,measuring) the temperature at a predetermined sample rate (e.g., 10times in a power update period, 1 second, in the specific embodiment).Then, an average of the 10 samples is calculated and compared to theaverage of the previous 10 samples. The difference between the averagesof the first 10 measured temperatures and the previous 10 measuredtemperatures is then divided by the power update period to obtain anaverage measured temperature. The derivative of the average measuredtemperature is then calculated to arrive at the calculated ramp rateT'(k). The ramp rate error Err_(RRate) may then determined by taking thedifference between the constant-valued T'_(des) (T(k)) and thecalculated ramp rate T'(k) in the specific embodiment (step 594). Theabove embodiment is an example of one numerical differentiationtechnique that may be used, but other techniques that may be moresophisticated also can be used in other embodiments. In otherembodiments, other sample rates also may be used.

To elaborate on step 596, an exemplary control function used in thespecific embodiment is given by the following equation:

    P(k+1)=P.sub.model [T(k),T'.sub.des (T(k))]+K.sub.p *[T'.sub.des (T(k))-T'(k)]

where k is the current time step and k+1 is the next time step. P(k+1)is the power that will be supplied to the heater at the next time step.P_(model) [T(k), T'_(des) (T(k))], which is a function of the desiredramp rate and measured temperature, is some modeled approximation of thenecessary power to give a ramp rate of T'_(des) (T(k)) at a temperatureT(k). K_(p) is a control gain constant (in Watts/(° C./second)) that isuser-defined and multiplied with the ramp rate error Err_(RRate). In thespecific embodiment, P_(model) [T(k),T'_(des) (T(k))] can beapproximated as P(k). This approximation is particularly true for slowsystems such as the resistive heater with large thermal mass of thepresent invention. The control function is then approximated by thefollowing equations:

    P(k+1)=P(k)+K.sub.p *[T'.sub.des (T(k))-T'(k)]

    P(k+1)-P(k)=K.sub.p *[T'.sub.des (T(k))-T'(k)]

Because the response of the heater is slow, there is a lag between thetime power is adjusted and the time when the adjustment produces thedesired result. For example, if the temperature of the heater is stableand the desired ramp rate is positive, the control will increase powerto the heater. The temperature will not, however, immediately riseaccording to the desired ramp rate. The control will then at the nexttime step further increase power. It will continue to increase poweruntil the desired ramp rate is met. By that time, however, the suppliedpower could be much greater than that needed to maintain the desiredramp rate. The ramp rate will continue to increase beyond its desiredvalue. This is called overshoot. The controller will react by reducingpower, and slowly the ramp rate will decrease. Once again, thecontroller can act faster than the heater, so it will reduce power toomuch and the ramp rate will decrease beyond its desired value. This isoscillation. Over time, the magnitude of the oscillations will decreaseand the ramp rate will reach a constant, steady-state value. Because allreal systems undergo small disturbances, there will also be a smallsteady-state error.

The value of K_(p) determines the size of the overshoot and thesteady-state error. If K_(p) is large, the system will be moreoscillatory, but steady-state error will be small. If K_(p) is small,the opposite is true. Typically, K_(p) can be large because Derivativecontrol can be used to damp the system's response, i.e. reduce overshootand oscillation. Steady-state error can be reduced by using Integralcontrol, but this tends to increase overshoot and oscillation and ispreferably avoided in this control algorithm. In this case, derivativecontrol is not available. It would require numerically calculating thesecond derivative of the temperature. Because the signal-to-noise ratioof the thermocouple signal is low, its second derivative can not becalculated reliably. Therefore, the present invention uses a large K_(p)to reduce steady-state error and a saturation function (step 598)instead of derivative control to dampen the system response. Thesaturation function effectively schedules the gain K_(p) such that K_(p)is inversely proportional to the ramp rate error, Err_(RRate). Duringthe transient portion of the system response, when errors are larger andovershoot can occur, the effective gain is small. In steady-state,errors are small, so the effective K_(p) is large.

The exemplary saturation function used to dampen system response isgiven by the following equations (step 598). For these equations, P(k+1)refers to the power defined by the control equation given above. P₁(k+1) is the actual power supplied to the heater. P'_(max). is thepredetermined maximum allowable change in supplied power from one timestep to the next. The exemplary saturation function is as follows:

if |P(k+1)-P(k)|>P'_(max),

then P₁ (k+1)=P(k)-P'_(max) for P(k+1)>P(k)

and P₁ (k+1)=P(k)-P'_(max) for P(k+1)<P(k)

else P₁ (k+1)=P(k+1)

A new term K_(peff) (k) can now be defined as the effective gain of thecontroller at time step k. Clearly, if P₁ (k+1)=P(k+1) the effectivegain at time k equals the gain K_(p). But if the saturation function isapplied, K_(peff) (k) is defmed by substituting P(k+1) for P₁ (k+1) inthe equations above and combining them with the equation:P(k+1)=P_(model) [T(k),T'_(des) (T(k))]+K_(p) *[T'_(des) (T(k))-T'(k)].The term K_(peff) (k) is as follows:

P'_(max) =K_(peff) (k)*Err_(RRate) (k);

K_(peff) (k)=P'_(max) /Err_(RRate) (k).

By making the effective gain small when the ramp rate error is large,overshoot and oscillation in the response are minimized by thissaturation function. This reduces the likelihood of damage to the heaterfrom poor ramp rate control. Accordingly, the ramp control algorithm ofheater control subroutine 167 dampens the system's response when largeramp rate errors occur, thereby resulting in more efficient temperaturecontrol.

A plasma control subroutine 170 comprises program code for setting themagnetron power levels and mode (CW or pulsed). In alternativeembodiments having RF plasma systems, plasma control subroutine 170 alsocould include program code for setting low- and high-frequency RF powerlevels applied to the process electrodes in chamber 15, and for settingthe low-frequency RF frequency employed. Of course, some embodiments mayhave one plasma control subroutine 170 used for microwave power levelsand another plasma control subroutine 170 used for RF power levels. Likethe previously described chamber component subroutines, plasma controlsubroutine 170 is invoked by chamber manager subroutine 157a.

A plasma control subroutine 170 comprises program code for setting andadjusting the magnetron power levels and mode (CW or pulsed). Inalternative embodiments having RF plasma systems, plasma controlsubroutine 170 also could include program code for setting low- andhigh-frequency RF power levels applied to the process electrodes inchamber 15, and for setting the low-frequency RF frequency employed. Ofcourse, some embodiments may have one plasma control subroutine 170 usedfor microwave power levels and another plasma control subroutine 170used for RF power levels. Like the previously described chambercomponent subroutines, plasma control subroutine 170 is invoked bychamber manager subroutine 157a. In embodiments having gate valve 280,plasma control subroutine 170 also includes program code for opening andclosing of gate valve 280 to coordinate with the setting/adjusting ofmicrowave power levels. Alternatively, the system software may have aseparate gate valve control subroutine in embodiments having gate valve280.

An endpoint detect control subroutine 159 includes program code formanaging endpoint detection by controlling a light source and a lightdetector, receiving data from the light detector for use in comparinglight intensity changes from absorbance, and optionally stopping thecleaning process upon detecting a predetermined light intensity level orraising a flag indicating the endpoint of the cleaning process. Endpointdetect control subroutine 159 also may be invoked by chamber managersubroutine 157a. Endpoint detect control subroutine 159 is included forthose embodiments using the endpoint detection system described below.It is recognized that embodiments not having an endpoint detectionsystem would not need to use or have endpoint detect control subroutine159.

Optionally, a gettering control subroutine 169 may be included that canbe invoked by chamber manager subroutine 157a. Gettering controlsubroutine 169 includes program code for controlling gettering processesthat may be used for chamber seasoning, post-clean fluorine gettering,etc. In some embodiments, gettering control subroutine 169 can invokespecified software built into the clean recipe to facilitate getteringcontrol in combination with the clean recipe used.

The CVD system description presented above is mainly for generalillustrative purposes and should not be considered as limiting the scopeof the present invention. The exemplary CVD system 10 is a single-wafervacuum chamber system. However, other CVD systems that aremultiple-wafer chamber systems may be used in other embodiments of theinvention. It should be understood, however, that although certainfeatures of the invention are shown and described as part of a CVDchamber in a multichamber processing system, the invention is notnecessarily intended to be limited in this manner. That is, theinvention can be used in a variety of processing chambers, such as etchchambers, diffusion chambers or the like. Variations of the abovedescribed system such as variations in design, heater design, locationof RF power connections, software operation and structure, specificalgorithms used in some software subroutines, configuration of gas inletlines and valves, and other modifications are possible. Additionally,other plasma CVD equipment such as electron cyclotron resonance (ECR)plasma CVD devices, induction coupled RF high density plasma CVDdevices, or the like may be employed. The dielectric layers and methodsfor forming such layers for use in the present invention should notnecessarily be limited to any specific apparatus or to any specificplasma excitation method.

As shown in FIGS. 2 and 3, CVD apparatus 10 generally includes anenclosure assembly 200 having vertically movable heater (wafer supportpedestal or susceptor) 25 for supporting a semiconductor wafer within avacuum chamber 15. Process gas(es) are delivered into chamber 15 toperform various deposition and etching steps on the wafer. A gasdistribution system 205 (FIGS. 2-6C) distributes process gases from gassources 90 (FIG. 1C) onto the wafer, and an exhaust system 210 (FIGS.2-4) discharges the process gases and other residue from chamber 15. CVDapparatus 10 further includes a heater/lift assembly 30 (FIGS. 1A, 9-15)that includes heater 25 for heating the wafer and for lifting the waferupwards into a processing position within chamber 15. An integral remotemicrowave plasma system 55 (FIGS. 1A and 16) is also provided in CVDapparatus 10 for periodic chamber cleaning, wafer cleaning, ordepositing steps.

As shown in FIG. 2, CVD apparatus 10 further includes a liquid coolingsystem 215 for delivering coolant to various components of the chamber15 to cool these components during the high temperature processing.Liquid cooling system 215 acts to decrease the temperature of thesechamber components to minimize undesired deposition onto thesecomponents due to the high temperature processes. Liquid cooling system215 includes a pair of water connections 217, 219 that supply coolingwater through the heater/lift assembly 30 and a coolant manifold (notshown) for delivering coolant to the gas distribution system 205(discussed below). A waterflow detector 220 detects the waterflow from aheat exchanger (not shown) to enclosure assembly 200. Preferredembodiments of the individual systems of apparatus 10 will be describedin further detail below.

A. Enclosure Assembly

Referring to FIGS. 2 and 6A-C, enclosure assembly 200 is preferably anintegral housing made from a process-compatible material, such asaluminum or anodized aluminum. Enclosure assembly 200 includes an outerlid assembly 225 for delivering process and clean gases through an inlettube 43 to an inner lid assembly 230 within assembly 200. Inner lidassembly 230 functions to disperse the gases throughout chamber 15 ontoa wafer (not shown) supported on heater 25. As shown in FIG. 2, a lidcover 233 provides access to the components on the top of enclosureassembly 200 (i.e., outer lid assembly 32), and shields the operatorfrom exposure to high temperatures during system operation. For SACVDprocesses, lid cover 233 preferably includes a cutout 235 to allowclearance for lid clamps 237 that ensure gas integrity of the chamber15. Lid cover 233 generally remains closed during most process stepsunless the chamber is opened, for example, to perform a preventivemaintenance chamber cleaning, thereby breaking the vacuum and bringingthe chamber to atmospheric pressure. A lid hinge 239 includes a lockingratchet mechanism 241 to prevent the lid cover 233 from falling closed.

As shown in FIG. 2, enclosure assembly 200 defines a vacuum lock door(not shown) and a slit valve opening 243 through which a wafer loadingassembly (not shown) transports a wafer W into process chamber 16 andloads wafer W onto heater 25. The wafer loading assembly is preferably aconventional robotic mechanism disposed within a transfer chamber (notshown) of the multichamber processing system. A suitable robotictransfer assembly is described in commonly assigned U.S. Pat. No.4,951,601 to Maydan, the complete disclosure of which is incorporatedherein by reference.

Referring to FIGS. 3, 4, 7A and 7B, the inside wall 245 of enclosureassembly 200 around chamber 15 is covered with a chamber liner 250,which rests on a shelf 252 of enclosure assembly 200. Chamber liner 250serves to inhibit process gases from flowing to the back side of thewafer. In addition, since heater 25 has a smaller diameter thanenclosure assembly 200, liner 250 inhibits the flow of process gasesbelow heater 25 to the lower portion of chamber 15. Accordingly,undesired deposition onto the bottom of heater 25 and the lower portionof chamber 15 is minimized. Further, liner 250 provides thermalinsulation between the aluminum walls of enclosure assembly 200 and theedge of the wafer on heater 25, in order to prevent wafer edge coolingduring high temperature processing. During high temperature processing,liner 250 prevents excessive heat loss from the hotter edges of thewafer on heater 25 (e.g., about 550-600° C.) to the cooler surroundingchamber walls (e.g., about 60° C.). Without liner 250, the heat effectsat the edge of the wafer may adversely affect temperature uniformityacross the wafer and lead to non-uniform deposition. Liner 250preferably comprises an inner portion 253 formed of a process-compatiblematerial that is well suited for high temperature processes (e.g.,greater than about 500° C.). Preferably, inner portion 253 of liner 250comprises a ceramic material, such as aluminum nitride, alumina, or thelike, with alumina being the preferred material. Inner portion 253 willusually have a thickness of about 0.1 to 1 inch and preferably about 0.2to 0.3 inch.

Liner 250 preferably comprises an outer portion 255 that comprises amaterial that is less susceptible to cracking than ceramic, such asaluminum. Outer portion 255 rests on shelf 252 of enclosure assembly,and includes an annular lip 254 for supporting inner portion 253 ofliner 250. In a particularly preferred embodiment, outer portion 255includes a plurality of circumferentially spaced vertical struts 257that define inner air gaps 259 therebetween, as shown in FIGS. 7A and7B. Air gaps 259 facilitate insulation of the inner portion 253 of liner250 from the outer chamber walls to increase wafer temperatureuniformity (otherwise the outer edge of the wafer could cool down due tothe surrounding chamber wall temperature, which is cool relative to theheater and wafer temperature). In addition, air gaps 259 providethickness to liner 250 so that it can bridge the gap between the outerchamber walls and heater 25 while minimizing the cracking or otherthermal damage that may occur with a thicker liner 250. Outer portion255 of liner 250 usually has a thickness of about 0.5 to 2 inches withan air gap 259 thickness of about 0.2 to 1.5 inches, and preferablyabout 0.9 to 1.1 inch with an air gap 259 thickness of about 0.6 to 0.9inch. An annular cover 261 is positioned on the upper surface of outerliner 255 to form the lower wall of a pumping channel 40 (discussedbelow). Annular cover 261 preferably comprises a ceramic material, suchas aluminum oxide or aluminum nitride, to shield the aluminum outerportion 255 of liner 250 from process gases and the heat within pumpingchannel 40.

In an alternative embodiment (not shown), liner 250 only comprises innerceramic portion 255 resting on shelf 252 of enclosure assembly andannular cover 261 forming the bottom of pumping channel 40. In thisembodiment, outer portion 255 is replaced with an air gap (not shown)between ceramic portion 255 and the inside wall of enclosure assembly.The air gap insulates the high temperature wafer from the cooler wallsof the enclosure assembly, and it provides thickness to liner 250 tobridge the gap between the chamber walls and heater 25.

B. Gas Distribution System

Referring to FIGS. 2 and 6A-C, outer lid assembly 225 generally includesa lid or base plate 265, a coolant manifold (not shown), a clean gasmanifold 270 that includes conduit 47, gas mixing box 273 for mixing andinjecting process gas(es) and cleaning gas(es) through inlet tube 43 tothe processing chamber 15, and a gate valve 280 for selectivelydistributing cleaning and/or process gases to gas mixing box 273. Ofcourse, it should be clearly understood that gate valve 280 is optional,and that outer lid assembly 225 can be modified to selectivelydistribute cleaning and/or process gases to box 273 without a gatevalve. As shown in FIG. 4, gas mixing box 273, clean gas manifold 277and gate valve 280 are preferably fastened, e.g., bolted, to the topsurface of base plate 265. First and second gas passages 83, 85 aremounted to the exterior of plate 265, and extend into gas mixing box273. Gas passages 83, 85 each have inlets suitably coupled to sources 90of gas (see FIG. 1C), such as ozone, TEOS, TEPO, helium, nitrogen, cleangas, or the like, and outlets (not shown) in communication with a mixingarea 93 within box 273 for mixing the gases prior to delivering themthrough inlet tube 43 into the inner lid assembly 230.

It should be noted that for plasma processes, CVD apparatus 10 willfurther include a gas feed-through box (not shown) housing gas passages83, 85 to enable the application of high voltage RF power to the gas boxwithout gas breakdown, and without gas deposition in the gasdistribution system. A description of an exemplary gas feed-through boxcan be found in U.S. Pat. No. 4,872,947 to Wang, the complete disclosureof which is incorporated herein by reference.

As shown in FIG. 6A, clean gas manifold 270 includes conduit 47 forreceiving gas(es) from inlet 290, and directing these gas(es) through afluid passage 293 into gas mixing box 273. Gate valve 280 includes avalve plug (not shown) seated within passage 293 for selectivelyallowing or preventing the gases from passing through conduit 47 intogas mixing box 273. Gate valve 280 may be manually operated by actuatinghandle 281, or gate valve 280 may be controlled by processor 50. Duringcleaning (discussed below), gate valve 280 is configured to allow theclean gases from plasma system 55 to pass into box 273, where they aredirected through inlet tube 43 into chamber 15 to etch the wafer or theinner chamber walls and the other components of apparatus 10.

As shown in FIG. 3, clean gas manifold 270 is constructed integral tothe top part of enclosure assembly 200 of apparatus 10, with conduit 47having an appropriate bend or curve from the top toward the side ofchamber 15. Conduit 47 of manifold 270 has an opening into a passageintegrally formed within a side wall of enclosure assembly 200 ofapparatus 10, which may become heated due to the high temperatures atwhich heater 25 operates. This passage is equipped with an internalliner 291 that serves to protect the inner surfaces of the passage inenclosure assembly 200 from corrosion and etching from the clean gasradicals entering from an applicator tube 292. Liner 291 also preventsrecombination of radicals in the clean gas. Clean gases are introducedinto applicator tube 292 from an inlet 57. Radicals are created fromclean gases in applicator tube 292 by microwave energy radiated from amagnetron in plasma system 55, which is advantageously located towardthe bottom of chamber 15 in enclosure assembly 200. The location ofsystem 55 at the bottom of apparatus 10 facilitates servicing of chamber15 for preventive maintenance cleanings, repairs, etc. In particular,opening the lid of apparatus 10 in order to perform preventivemaintenance cleanings is easily done, since the bottom-mounted remotemicrowave plasma system 55 is not located on top of the lid of apparatus10. Microwave plasma system 55 is discussed in further detail below. Asshown in FIGS. 3 and 4, inlet tube 43 preferably includes an innerpassage 295 for delivering process gases into chamber 15, and an outer,annular passage 297 in communication with passage 293 for directingcleaning gases into the chamber.

The coolant manifold, which may be fastened to the top or side surfaceof base plate 265, receives coolant fluid, such as water or aglycol\water mixture, from the heat exchanger. The coolant isdistributed from the coolant manifold through an annular coolant channel93 (FIGS. 4 and 5) in base plate 265 to convectively and conductivelyremove heat from plate 265 and the components of inner lid assembly 230during processing (discussed in further detail below).

As shown in FIGS. 2 and 5, inner lid assembly 230 generally includesbase plate 265, a blocker or gas dispersion plate 301 and a showerheador gas distribution plate 20 for dispersing process and clean gases intochamber 15. Plates 301, 20 are preferably formed from aprocess-compatible material that is capable of withstanding hightemperature processes. For example, plates 301, 20 may comprise aceramic material such as aluminum oxide or aluminum nitride (AlN), or ametal, such as aluminum or anodized aluminum. Preferably, the plates301, 20 comprise a metal, such as aluminum or anodized aluminum, tominimize gas deposition on the surfaces of plates 301, 20. In aparticularly preferred embodiment, gas dispersion plate 301 comprisesanodized aluminum and gas distribution plate 20 comprises aluminum. Gasdistribution and gas dispersion plates 301, 20 are each directlyfastened to a lower surface of base plate 265. Preferably, gasdistribution and dispersion plates 20, 301 are affixed to lower surfaceof base plate 265 with a plurality of threaded mounting screws 303, 305,respectively. Mounting screws 303, 305 provide a relatively tight,surface-to-surface contact between contact surfaces of gas distributionand dispersion plates 20, 301, respectively, and lower surface of baseplate 265 to facilitate conductive heat exchange therebetween (discussedin greater detail below). The mounting screws 303, 305 comprise aprocess-compatible material, such an nickel, Hasteloy™, Haynes™ or thelike.

Referring to FIGS. 4 and 5, gas distribution plate 20 is a substantiallyflat plate 311 having an outer flange 313 with a plurality of holes 315for receiving mounting screws 305 to provide engagement of the contactsurface of plate 20 with lower surface of base plate 265. Base plate 265includes an outer annular stand-off 316 that spaces gas distributionplate 20 from the bottom surface of 265 and forms a chamber 317 (seeFIG. 4) between these two plates for dispersing the process gasuniformly through a plurality of gas distribution holes 315 onto asemiconductor wafer. Alternatively, gas distribution plate 20 maycomprise a dish-shaped device (not shown) having a centrally disposedcavity defined by a side wall and a base wall.

The size and arrangement of gas distribution holes 315 will varydepending on the process characteristics. For example, the holes 315 maybe uniformly spaced to provide a uniform distribution of gases onto thewafer. On the other hand, holes 315 may be non-uniformly spaced andarranged, if desired. Holes 315 will usually have a diameter in therange of about 5-100 mil and preferably in the range of about 10-50 mil.Preferably, gas distribution holes 315 are designed to promoteuniformity of deposition on the semiconductor wafer. The holes (as wellas the manifold temperature, discussed above) are also designed to avoidthe formation of deposits on the manifold outer (bottom) surface and, inparticular, to prevent the deposition of soft deposits on that surfacewhich could flake off and drop onto the wafer during and afterprocessing. In an exemplary embodiment, the hole array is one ofgenerally concentric rings of holes 315. The distances between adjacentrings (ring-to-ring spacings) are approximately equal, and thehole-to-hole spacing within each ring is approximately equal. A morecomplete description of a suitable arrangement for the gas distributionholes is described in commonly assigned U.S. Pat. No. 4,872,947 to Wang,the complete disclosure of which has previously been incorporated byreference.

Gas dispersion plate 301 is a generally circular disk 321 including aplurality of gas dispersion holes 325 for dispersing the gastherethrough into the chamber 317 formed between outer stand-off 316 andgas distribution plate 20. Base plate 265 preferably includes a second,inner stand-off 318 for spacing dispersion plate 301 from base plate 265and for allowing gas passing through base plate 265 to disperse into achamber 320 (see FIG. 4) formed between stand-off 318 and plate 301.Alternatively, gas dispersion plate 301 may define a recess (not shown)for forming chamber 320 rather than stand-off 318. Dispersion holes 325will usually have a diameter of about 0.02-0.04 mm. Of course, it willbe recognized by those skilled in the art that dispersion plate 301 maybe included in preferred embodiments of the invention. However, theprocess gases may be passed directly from base plate 265 into chamber317 of gas distribution plate 20, in other embodiments.

As shown in FIGS. 4 and 5, base plate 265 is an integral, single-pieceelement that functions to deliver process gas(es) to gas dispersionplate 301 and to mount the entire inner lid assembly 230 to themainframe unit of the processing chamber. In RF plasma processes, innerlid assembly 230 will also include an isolator (not shown) thatelectrically insulates the chamber lid from ground and isolates thechamber body from the RF gas box (not shown). An exemplary lid assemblyfor use with RF plasma processes is described in U.S. Pat. No. 4,872,947to Wang, the disclosure of which has previously been incorporated byreference.

As shown in FIG. 8, base plate 265 has a lower surface 321 that defmesan annular pumping channel 40 for exhausting the deposition gases(discussed in detail below). As shown in FIGS. 4 and 5, base plate 265defines a central hole 327 in communication with inlet tube 43 forreceiving the mixed process gases from gas mixing box 273. Hole 327 isalso in communication with recess 311 of gas dispersion plate 301 fordispersing the gas across plate 301 to holes 315. Base plate 265 furtherdefines a coolant passage 93 having an inlet 331 and an outlet 333coupled to the cooling system 215 for directing coolant fluid throughportions of plate 215 to convectively cool these portions of plate 265.Preferably, coolant passage 93 is formed within portions of base plate265 that are relatively close to mounting screws 303, 305. Thisfacilitates conductive cooling through contact surfaces of dispersionand distribution plates 301, 20 and lower surface 326 of base plate 265.A more complete description of exemplary designs for coolant passage 93can be found in commonly assigned, co-pending U.S. application Ser. No.08/631,902, filed Apr. 16, 1996 (Attorney Docket No. 1034), the completedisclosure of which is incorporated herein by reference, and in commonlyassigned U.S. Pat. No. 4,872,947 to Wang, the complete disclosure ofwhich has previously been incorporated by reference.

Referring to FIG. 5, base plate 265 further defines an annular recess343 surrounding central hole 327 and an annular cap 345 disposed withinrecess 343 fastened to base plate 265 above coolant passage 93.Preferably, annular cap 345 is welded to upper surface of base plate 265to provide a tight seal over passage 93, thereby effectively preventingcoolant leakage from passage 93. With this configuration, passage 93 isformed relatively close to gas distribution and dispersion plates 20,301. In addition, passage 93 is fabricated by forming a groove in theupper surface of base plate 265, thereby decreasing the cost andcomplexity of manufacturing plate.

Referring now to FIGS. 6B and 6C, an alternative embodiment of inner lidassembly 230' will now be described. Similar to the previous embodiment,lid assembly 230' includes a base plate 265, a gas dispersion plate 301and a gas distribution plate 20 for dispersing process and clean gasesinto chamber 15. In addition, base plate 265 includes an annular coolantchannel 500 for receiving a coolant liquid, such as water, to cool baseplate 265 and the other components of lid assembly 230'. In thisembodiment, base plate 265 further includes an additional annular fluidchannel 502 extending around central hole 295 above gas dispersion plate301 for exchanging heat with the portion of base plate 265 immediatelyabove gas dispersion and gas distribution holes 325, 315.

Inner lid assembly 230' includes a plurality of bypass passages 510extending from chamber 320 between base plate 265 and gas dispersionplate 301 to vacuum chamber 15. Bypass passages 510 offer a lowerresistance to fluid flow than gas dispersion and gas distribution holes325, 315. Accordingly, a large portion of the gas flowing into chamber320 will pass through bypass passages 520 directly into the vacuumchamber 15. In an exemplary embodiment, bypass passages 510 arepreferably spaced circumferentially around base plate 265 to uniformlydeliver gases into the chamber 15 (see FIG. 6C). In a preferred use ofthis embodiment, cleaning gases, such as NF₃, pass into chamber 320 andthrough gas dispersion and gas distribution holes 325, 315,respectively. In addition, a portion of the cleaning gases pass throughbypass passages 510 directly into chamber 15 to facilitate the deliveryof the cleaning gases into chamber 15.

In this embodiment, vapor deposition apparatus 10 will preferablyinclude a control system, such as a valve coupled to a controller (notshown) for preventing (or at least inhibiting) gases from passingthrough bypass passages 510. For example, during processing, it istypically desired that the process gases pass through gas distributionand dispersion holes 325, 315 to uniformly disperse onto the wafer.Thus, the valve will be closed to prevent the process gases from passingthrough bypass passages 510. When the chamber is cleaned, the valve willbe opened to quickly deliver at least a portion of the cleaning gasesinto the chamber. This increases the speed and efficiency of thecleaning process, which reduces the down time of apparatus 10. Ofcourse, it will be recognized that process gases may also be deliveredthrough bypass passages 510, if desired.

C. The Exhaust System

Referring to FIGS. 2-4, a pump (not shown) disposed exterior to CVDapparatus 10 provides vacuum pressure to draw both the process and purgegases, as well as residues, out of chamber 15 and through annularpumping channel 40, where they are discharged from apparatus 10 along adischarge conduit 60. As shown in FIG. 8, the deposition and clean gasesare exhausted radially outward over the wafer W (shown by arrows 351)through an annular slot-shaped orifice 355 surrounding the chamber 15and into pumping channel 40. The annular slot-shaped orifice 355 andchannel 40 are preferably defined by the gap between the top of thechamber's cylindrical side wall 17 (including inner portion 253 of thechamber liner 250, see FIGS. 3 and 4) and the bottom of base plate 265.From the pumping channel 40, the gases flow circumferentially aroundchannel 40 (shown by arrows 357) and through a downwardly extending gaspassage 361, past a vacuum shut off valve 363 (whose body is preferablyintegrated with the lower chamber body), and into discharge conduit 60which connects to an external vacuum pump (not shown).

Alternatively, CVD apparatus 10 may include a separate pumping plate(not shown) having a plurality of gas holes that directly communicateprocess chamber 15 with pumping channel 40. In this embodiment, the gasholes are circumferentially spaced around the central opening of thechamber to facilitate the uniform discharge of process gas through theholes. To accommodate the relative positions of inlets and outlets, gasholes may extend in a radially outward direction from inlets to outletsrelative to central opening. This radial orientation of holes alsocontributes to a substantially uniform discharge of the process andpurge gases and exhausted residues from the processing chamber 15. Amore complete description of this type of pumping plate can be found incommonly assigned co-pending U.S. application Ser. No. 08/606,880, filedFeb. 26, 1996 (Attorney Docket No. 978), the complete disclosure ofwhich is incorporated herein by reference.

Referring to FIGS. 2 and 3, a valve assembly (throttle valve system) 369includes an isolation valve 371 and a throttle valve 373 disposed alongdischarge line 60 for controlling the flow rate of the gases throughpumping channel 40. The pressure within processing chamber 15 ismonitored with capacitance manometers 381, 383 (see FIG. 2) andcontrolled by varying the flow cross-sectional area of conduit 60 withthrottle valve 373. Preferably, processor 50 receives from manometers381, 383 signals that indicate the chamber pressure. Processor 50compares the measured pressure value with set-point pressure valuesentered by operators (not shown), and determines the necessaryadjustment of throttle valve 333 that is required to maintain thedesired pressure with in chamber 15. Processor 50 relays an adjustmentsignal through a controller 385 to a drive motor (not shown), whichadjusts throttle valve 373 to a proper setting corresponding to theset-point pressure value. Suitable throttle valves for use with thepresent invention are described in commonly assigned, co-pending U.S.applcation Ser. No. 08/672,891 entitled "Improved Apparatus and Methodsfor Controlling Process Chamber Pressure" (Attorney Docket Nos.891/DCVD-II/MBE), filed Jun. 28, 1996, the complete disclosure of whichis incorporated herein by reference.

Isolation valve 371 may be used to isolate process chamber 15 from thevacuum pump to minimize the reduction of chamber pressure due to thepumping action of the pump. Isolation valve 371, together with throttlevalve 373, may also be used to calibrate the mass flow controllers (notshown) of CVD apparatus 10. In some processes, liquid dopants arevaporized, and then delivered into process chamber 15 along with acarrier gas. The mass flow controllers are used to monitor the flow rateof the gas or liquid dopants into the chamber 15. During calibration ofthe MFCs, isolation valve 371 restricts or limits the gas flow tothrottle valve 373 to maximize the pressure increase in chamber 15,which facilitates MFC calibration.

D. Heater/Lift Assembly

Referring to FIGS. 9-15B, heater/lift assembly 30 will now be describedin detail. The heater/lift assembly 30 functions to lift the wafer intothe processing position with in vacuum chamber 15 and to heat the waferduring processing. At the outset, it should be noted that heater/liftassembly 30 may be modified for use, or directly placed into, a varietyof processing chambers other than the exemplary SACVD chamber describedand shown herein. For example, heater/lift assembly 40 may be used in asimilar CVD chamber that generates plasma with RF or microwave power, ametal CVD (MCVD) chamber, or other conventional or non-conventionalsemiconductor processing chambers.

Referring to FIGS. 9 and 13, heater/lift assembly 30 generally includesa resistively-heated wafer support pedestal or heater 25 attached toupper and lower support shafts 391, 393, a lift tube 395 circumscribingsupport shafts 391, 393 underneath heater 25 and a drive assembly 400for vertically moving the heater 25, shafts 200, 201 and lift tube 202within chamber 15. As discussed in detail below, heater 25 (and thewafer supported thereon) can be controllably moved between a lowerloading/unloading position where they are substantially aligned withslot 243 in enclosure assembly 200 and an upper processing positionbeneath gas distribution plate 20 (FIGS. 3 and 4). As shown in FIG. 7,heater 25 includes an upper wafer support surface 403 surrounded by anannular raised perimeter flange 405 so that the wafer is accuratelylocated during processing. Wafer support surface 403 has a diameterapproximately equal to the diameter of wafer W at the depositiontemperature, e.g., at a temperature ranging from about 200-800° C. Thisdiameter will typically be about 6-8 inches (about 150-200 mm) for largesize wafers and about 3-5 inches (about 75-130 mm) for small sizewafers. Of course, other wafer sizes such as those with about 12 inch(about 300 mm) diameters would be within the scope of the invention withappropriate modification of the chamber, the chamber lining 250, andsupport heater 25.

Support heater 25 preferably comprises a disk made from aprocess-compatible material that is capable of withstanding relativelyhigh processing temperatures, i.e., up to 600-800° C. or higher. Thematerial should also be resistant to deposition from the reactivechemistries associated with the high temperature deposition, as well asresistant to etching by the radicals in the clean gas. Suitablematerials for heater 25 are ceramics, such as aluminum nitride, aluminumoxide or the like. Aluminum nitride ceramic is the preferred materialfor the heater 25 because it has high thermal conductivity, excellentcorrosion resistance, and excellent tolerance of thermal shock. Thus, ina particularly preferred embodiment, the entire outer surface of heater25 comprises aluminum nitride. Aluminum nitride has high temperaturecapabilities and high resistance to fluorine and ozone chemistries usedin chamber 15. Use of aluminum nitride, as compared to stainless steelor aluminum materials, for heater 25 also has less backside metalcontamination in the processed wafer, resulting in more reliabledevices. In addition, aluminum tends to react with the fluorinecontaining compounds typically used in cleaning gases to form a layer ofan aluminum fluoride compound that may eventually build-up and flake offinto the chamber or onto the wafer, resulting in contamination(discussed in further detail below). Constructing the heater 25 ofaluminum nitride effectively eliminates this problematic reaction duringcleaning.

Referring again to FIG. 7, drive assembly 400 may include a variety ofdriving mechanisms, including a pneumatic cylinder, controllable motoror the like. Preferably, a stepper motor 407 coupled to the heater via asuitable gear drive 409 operates to vertically drive heater 25, shafts391, 393 and lift tube 395 in controlled increments between theloading/unloading and processing positions. Drive assembly 400 alsoincludes upper and lower bellows 411, 413 attached between the end ofshaft 391 and the bottom of the processing chamber to allow forsubstantially free vertical movement of heater 25. In addition, bellows411, 413 allow some angular movement to ensure that the gas distributionfaceplate 20 and the heater 25 are substantially parallel duringprocessing.

Referring to FIGS. 4, 9 and 13, lift tube 395 surrounds the lowerportion of upper shaft 391 and assists in insulating upper bellows 411from thermal energy radiating from shaft 391, heater 25 and the insideof processing chamber 15. Lift tube 395 usually comprises an aluminumshaft 418, an annular strike plate 420 resting on the upper surface ofshaft 418 and an annular flange 422 that mounts plate 420 to shaft 418.Flange 422 and strike plate 420 are preferably formed from a materialcapable of withstanding high temperatures, such as aluminum nitride oraluminum oxide (Al₂ O₃ in its ceramic or alumina form). Flange 422 andstrike plate 420 insulate the aluminum shaft 418 from the heater tominimize warping or fusing of shaft 418 to heater shaft 391 or to theprocess chamber. In an exemplary embodiment, lift tube 395 includes aspring (not shown), such as a wave spring, loaded between flange 422 andstrike plate 420 to prevent or at least inhibit rattling of the strikeplate 420.

As shown in FIGS. 4 and 13, a plurality of wafer-support/lift fingers430, usually at least two and preferably four, are slidably mountedwithin guide studs 432 spaced about the periphery of heater 25. Fingers430 extend downward below heater 25 so that strike plate 420 may engagefmgers 430 and lift them above the upper surface of heater 25 forloading and unloading wafers. Lift fingers 430 are preferably made of aceramic material, such as aluminum oxide, and generally have a doubletruncated cone shaped head (not shown) The four lift finger guide studs432 are preferably not uniformly distributed about the heater 25, butinstead form a rectangle having at least one side that is wider than thewidth of the robot blade, which is typically a thin, flat bar (notshown), around which the lift fmgers 430 must lift the wafer. The bottomend of the lift fingers 430 are rounded. The fingers 430 have arelatively thick diameter of about 100-200 mil, preferably about 150mil, and a relatively short length of about 1-3 inches, preferably 2inches, to minimize finger binding to the heater during processing.

In use, the robot blade (not shown) transfers the wafer to the chamber15 when the heater 25 is in position opposite slit 243 (or actually justbelow slit 243). The wafer is supported initially by lift fmgers 430,which are lifted above heater 25 with strike plate 420. As lift fingers430 rise along with heater 25, they encounter a stop (not shown). Asheater 25 continues to rise to the processing position opposite gasdistribution faceplate 20, lift fingers 430 sink into guide studs 432within heater 25 and the wafer is deposited onto wafer support surface403 within annular flange 405. To remove the wafer from chamber 15, theabove steps are performed in reverse.

Referring again to FIG. 9, a resistive heater coil assembly 440 ishoused within heater 25 for transferring heat to the wafer duringprocessing. Upper and lower support shafts 391, 393 support the heater25 and house the necessary electrical connections to the heater coilassembly 440 within a hollow core 445 (discussed below). Upper supportshaft 391 is made of a ceramic material capable of withstandingrelatively high processing temperatures. Preferably, shaft 391 will befabricated from diffusion-bonded aluminum nitride, which preventsdeposition onto, as well as attack by chemistries used in chamber 15 of,the electrodes and electrical connections within shaft 391 that mightotherwise occur if the aluminum nitride were not present. Shaft 391 ispreferably diffusion-bonded to heater 25 to provide a gas-tight sealbetween heater 25 and shaft 391 such that the hollow core 445 of shaft391 is at ambient temperature and pressure (preferably atmosphericpressure, i.e., 760 torr or 1 atm). In other embodiments, hollow core445 may be at a pressure of about 0.8-1.2 atm and a temperature of about10-200° C., while chamber 15 may be at temperatures of at least about400° C. and pressures of about 20 mtorr to about 600 torr. Thisconfiguration helps to protect the electrodes and other electricalconnections from corrosion from the process and clean gases withinchamber 15. In addition, maintaining the hollow core 445 of shaft 391 atambient pressure minimizes arcing from the RF power source throughhollow core 445 to power leads or the aluminum shaft. This arcing thatmight otherwise occur in a vacuum is thus avoided.

Referring to FIGS. 9 and 10, upper support shaft 391 extends through anopening 453 in the lower surface of enclosure assembly 200, and iscoupled to a base 455 that provides a gas seal between shaft 391 andchamber 15. Upper support shaft 391 is fastened, e.g., bolted, to lowersupport shaft 393, which comprises a suitable process-compatiblematerial, such as aluminum or an aluminum alloy. Lower support shaft 393is preferably a water-cooled aluminum shaft. However, lower supportshaft 393 may also comprise a ceramic material, such as aluminum oxideor aluminum nitride. One or more sealing members 457, e.g., O-rings, arepositioned between shafts 391, 393 to maintain the gas seal between core445 and chamber 15. As shown in FIG. 9, lower support shaft 393 ismounted to a vertically movable support 461 on drive assembly 400 formoving the shafts 391, 393 and heater 25 between the loading andprocessing positions. Shaft 393 defines an inner coolant channel 463passing around the electrical connections to further insulate theseconnections from the high temperature of the shaft. Coolant channel 463has an inlet 464 and an outlet 466 coupled to water connections 217,219, respectively, of liquid cooling system 215. Coolant channel 463serves to maintain a relatively low temperature in the lower chamberarea to protect sealing member(s) 457. In an alternative embodiment,heater assembly 30 comprises a single shaft (not shown) that supportsheater 25 and extends through the lower opening 453 in enclosureassembly 200. In this alternative embodiment, sealing members 457 wouldnot be used.

Heater coil assembly 440 is configured to provide a temperature of atleast about 200-800° C. in chamber 15 at a rate of about 20° C./min.Referring to FIGS. 11 and 12, heater coil assembly 440 includes a heatercoil 471 embedded into the ceramic heater 25. The routing of the heatercoil 471 embedded in the heater base 25 preferably provides a singlecoil 471 that begins at one electrical contact 472 near the center ofheater 25, runs back and forth along one side of heater 25 towards itsperimeter, extends to the other side of heater 25, and then runs backand forth toward the center of heater 25 to a second electrical contact474. This loop pattern provides heating to maintain a generally uniformtemperature across the width of the plate while allowing for heatlosses. Preferably, heater coil 471 will provide a uniform temperaturedistribution of at least about +/-2° C. at 400° C. and at least about+/-8° C. at 600° C. across wafer support surface 403 of heater 25. In anexemplary embodiment, heater coil 471 will have a greater power densitynear the center of heater 25 to reduce the thermal gradient from heatershaft 391.

As shown in FIG. 14, heater coil assembly 440 preferably includes anembedded RF mesh ground plane electrode 473 connected to a plurality ofconductor lead wires 475 which extend through shaft 341 to a suitableelectrical energy source. Mesh ground plane element 473 is a molybdenummesh electrode which provides the ground path and plasma resistance inembodiments where plasma processes are used. Lead wires 475 preferablycomprise a conductive material that can withstand relatively highprocess temperatures, such as nickel, copper or the like. In anexemplary configuration, lead wires 475 are each nickel wires coupled toelectrode 473 by a metal insert 477 that is co-sintered into electrode473 to avoid brazing between ceramic and metal. Inserts 477 preferablycomprise a material with a relatively close thermal expansion match toaluminum nitride, such as molybdenum. As shown, the molybdenum inserts477 are each fastened, e.g., brazed, to a molybdenum plug 481, which isthen brazed to lead wire 475. All of the wires of the heater coil,whether primarily resistive or primarily conductive, are sheathed in thecontinuous insulating coating (such as described above) which toleratehigh temperatures so as to withstand casting of the aluminum nitrideheater body.

Referring to FIGS. 9, 15A and 15B, heater/lift assembly 30 includes atleast one thermocouple 491 for determining the temperature of heatingcoil 471. Thermocouple 491 includes an elongate tube 493 having a sensor495 (FIG. 9) inserted and held in contact with the underside of heater25 at a distance of about 0.25 inch from the bottom of the wafer. Tothat end, heater 25 includes a thermocouple guide 501 (FIG. 15A) brazedto heater element 473 for connecting sensor 495 of thermocouple 491 toelement 473. The thermocouple 491 is held in place by a slight springforce from a compression spring 503 (FIG. 15B), and provides a controlsignal for the temperature controller (not shown). Sensor 495 ispreferably disposed in a well 505 which is at atmospheric pressure,which enhances the heat transfer between the heating element 473 and thethermocouple 491 to provide a more accurate reading. The temperaturecontroller is a recipe-driven proportional integral differential (PID)controller which anticipates the recipe steps which are about to occurand alters the response characteristic of the heater to maintain auniform temperature profile. A vacuum seal and ground connection for thelower support shaft 393 is made along the side surface of shaft 393 (notshown) and connections to heater wire ends 511 and the thermocouple tubeend 513 are made at atmospheric conditions.

When the present invention is in use, a robot blade (not shown)transfers the wafer to the chamber 15 when the heater 25 is in positionopposite slit 243 (or actually just below slit 243). The heater 25 andwafer are lifted into the processing position by drive assembly 400 andlift fingers 430 sink into guide studs 432 within heater 25 so that thewafer is deposited onto wafer support surface 430 within annular flange405 of heater 25 (FIGS. 4, 9 and 10). Process gases, such as TEOS andO₃, are directed through gas passages 83, 85 and mixed together inmixing area 93 of gas mixing box 273 (see FIGS. 3 and 6A-6C). The mixedgas is then delivered through inner passage 295 of inlet tube 43 andthrough central hole 327 of base plate 265 into chamber 320 above gasdispersion plate 301, where it disperses outward and flows through holes325 into chamber 317 above gas distribution plate 20 (see FIGS. 4 and5). Preferably, the gas is uniformly distributed through gasdistribution holes 315 onto the semiconductor wafer (not shown).

The temperature of the wafer on heater 25 is typically held above aminimum deposition temperature by heater coil assembly 440 so that theprocess gases will react together at the wafer surface and deposit alayer thereon. Specifically, an electric current is directed throughconductor wires 457 to resistive coil 473 to heat the wafer to atemperature of about 200-800° C., according to specific embodiments. Inthe preferred embodiment, the temperature is controlled by a feedbackcontrol system (described above for heater control subroutine 167) thatmaintains the ramp rate based on the current temperature in the chamber.During this process, inner lid assembly 230 receives heat from varioussources including the gases passing therethrough, the heatedsemiconductor wafer, and the wafer heating source. To maintain thecomponents of lid assembly 230 below the minimum deposition temperatureand thereby avoid gas reactions and deposition on these components, acoolant liquid is introduced into coolant channel 93 to remove heat frombase plate 265 and gas distribution and dispersion plates 20, 301.

During the deposition process, the vacuum pump is activated to generatevacuum pressure within pumping channel 40, thereby drawing the processgases and plasma residue out of processing chamber 15 through channel 40and exhaust port 361 (FIGS. 4 and 8). In addition, purge gas may bedirected generally upward into processing chamber 15 through the gapbetween susceptor 25 and inner portion 253 of liner 250. The purge gasminimizes leakage of process gas into the lower portion of apparatus 10and facilitates the removal of the process gas through port 361.

E. Integral Remote Microwave Plasma System

FIG. 16 is a simplified diagram of a remote microwave plasma system 55for cleaning the wafer and/or the process chamber, in accordance with anembodiment of the present invention. Microwave plasma system 55 producesa plasma remote from processing chamber 15 for use in efficientlyetching or cleaning a wafer in chamber 15 and/or components of chamber15, and possibly for use in depositions. Microwave plasma system 55includes applicator tube 292; a plasma ignition system (describedbelow); a microwave waveguide system (described below); optimizingelements including an impedance matching system 701 which may include anoptional phase detector 703 for embodiments requiring feedback forautomatic impedance matching, and a circulator 705 with a load 707; anda magnetron 711.

Magnetron 711 is a typical magnetron source capable of operating betweenabout 500-2500 Watts for continuous wave (CW) or pulsed output ofmicrowaves of about 2.45 Gigahertz (GHz) frequency. Magnetron 711 ispowered by power supply 110 (shown in FIG. 1C) which may be remotelylocated from magnetron 711. Of course, other magnetrons may be utilizedas well. Microwaves from magnetron 711 are transmitted to the microwavewaveguide system, which includes various lengths of straight and curvedwaveguide sections 715, 717 which may be connected together at joints719. Interspersed within the waveguide system are optimizing elementsthat work to provide low loss, maximum microwave transmission withminimized reflection losses and to protect the magnetron from damage dueto reflected power. The description below follows the desired directionof microwaves from magnetron 711 toward applicator tube 292.

In a specific embodiment, microwave plasma system 55 has magnetron 711connected to circulator 705 with load 707, as shown in FIG. 16.Circulator 705 allows only forward microwave transmission from magnetron711 toward applicator tube 292. Load 707 absorbs any power that might bereflected back from the waveguide system toward magnetron 711.Circulator 705 and load 707 thereby direct microwaves in the forwarddirection and protect magnetron 711 from damage from reflected power.Circulator 705 connects to waveguide section 715 that is connected tophase detector 703 connected to another waveguide section 715. Phasedetector 703, if utilized, is coupled via curved waveguide section 717to another waveguide section 715 having attached tuning or matchingsystem 701. Tuning system 701, which may use stub tuners or other tuningelements, provides plasma microwave system 55 with the ability to matchthe load at waveguide section 721 to 50 Ω, the characteristic impedanceof the waveguides. Tuning system 701 may provide fixed tuning, manualtuning, or automated tuning, according to specific embodiments. Forembodiments using automated tuning, phase detector 703 is a 3-diodearray which detects the phase of microwaves transmitted for feedback tomatching system 701, which intelligently and dynamically matches theload appropriately. In the specific embodiment, waveguide sections haverectangular cross-sections, but other types of waveguide also may beused.

As seen in FIG. 16, microwaves directed through the optimized waveguidesystem are transmitted from output waveguide section 721 to applicatortube 292, where a plasma is created. Applicator tube 292 has an inputfeed line 57 that receives reactive gases that are energized bymicrowaves from magnetron 711 via the waveguide system and otheroptimizing elements. Applicator tube 292 is a circular (or othercross-section) tube made of a composite or ceramic material, preferablyalumina, or other material resistant to etching by radicals in theplasma, according to a specific embodiment. In the specific embodiment,applicator tube 292 has a length of about 18-24 inches and across-sectional diameter of about 3-4 inches. Applicator tube 292 isdisposed through waveguide section 721, which is open at one end fortransmitting microwaves and is terminated at the other end with a metalwall. Microwaves are then able to be transmitted through the open end ofwaveguide section 721 to reactive gases inside applicator tube 292,which is transparent to microwaves. Of course, other materials such assapphire also may be used for the interior of applicator tube 292. Inother embodiments, applicator tube 292 may have a metal exterior and aninterior made of a composite or ceramic material and microwaves inwaveguide section 721 enter a window through the exterior of applicatortube 292 to the exposed interior of tube 292 to energize the reactivegases.

In the specific embodiment, a plasma may be ignited by plasma ignitionsystem which includes an ultraviolet (UV) lamp 731 and a UV power supply733, which may optionally be mounted on the metal wall of waveguidesection 721. Of course, UV power supply 733 may be mounted in variousother locations besides on the metal wall. Powered by UV power supply733, UV lamp 731 provides the initial ionization of the plasma withinapplicator tube 292. Microwave energy then sustains the ionization ofthe ignited plasma to produce the flow of radicals that enter inlet 290leading to chamber 15 via gate valve 280. Due to changes in load withinapplicator tube 292 from the introduction and ionization of reactivegases within tube 292, use of matching system 701 optimizes themicrowave energy coupling for efficiency. In preferred embodiments,matching system 701 includes at least one stub tuner under the controlof processor 50 or a controller unit for automated tuning. As mentionedabove, other conventional tuning elements also may be used in matchingsystem 701.

As discussed above, applicator tube 292 is mounted from and connected tothe bottom of the body of chamber 15 such that applicator tube 292outputs plasma radicals into inlet 290 of enclosure assembly 200, asseen in FIG. 3. Radicals are input through inlet 290 into the passage inenclosure assembly 200 which is equipped with liner 291, preferably madeof polytetraflouroethylene (PTFE). PTFE, which is commerciallyavailable, for example, as Teflon™ PTFE is resistant to etching ordeposition from the reactive chemistry input at inlet 290. Liner 291prevents fluorine radical recombination in the passage during cleanprocesses. In addition to PTFE, liner 291 also may be made of anyfluorinated material including fluorinated polymers such as PFA (whichis a polymer combining the carbon-fluorine backbone ofpolytetrafluouroethylene resins with a perfluoro-alkoxy side chain),fluorinated ethylene-propylene (TFE), or the like. The passage ispreferably circular in cross-section or other type of cross-section tomatch the cross-section of inlet 290 and applicator tube 292. From thislined passage in enclosure assembly 200, plasma radicals flow intoconduit 47 in clean gas manifold 270 to gate valve 280. Clean gasmanifold 270 is also constructed of PTFE. PTFE is preferred for cleaningapplications where fluorine radicals are produced in the plasma, sincePTFE is resistant to etching by fluorine radicals. Of course, both cleangas manifold 270 and liner 291 may be made of other materials (such asthose mentioned above for liner 291) which are resistant to theparticular chemistry depending on the reactive gases used.

In some embodiments, gate valve 280 isolates the clean processes fromthe deposition processes, as discussed above. Gate valve 280 normallyremains closed while chamber 15 is being used for deposition, reflow, ordrive-in steps. In the closed position, gate valve 280 preventsparticles in conduit 47 used for clean processes from contaminating thewafer during deposition processes, as well as reducing the "dead" volumeof conduit 47 and passage during deposition. If deposition at pressuresof between about 200-760 torr occurs with gate valve 280 open,deposition may be caused in applicator tube 292, leading tocontamination of the cleaning processes. Gate valve 280 is preferablymade of PTFE (or similar materials such as those discussed above forliner 291 and manifold 270) to minimize damage to or deposition onto theclosed valve 280 due to the reactive chemistries from conduit 47. In apreferred embodiment, gate valve 280 is a particle-grade gate valve. Inembodiments using gate valve 280, only when chamber 15 is used for awafer cleaning step or when a chamber cleaning is performed does gatevalve 280 open, allowing plasma radicals to flow into fluid passage 293of gas mixing box 273, as seen in FIG. 3. As mentioned above, in someembodiments gate valve 280 is not used at all. The plasma radicals thenmay flow through annular passage 295 and into chamber 15 via gasdistribution plate 20. Distribution plate 20 as well as various parts ofchamber 15 are thus cleaned. Residues and used cleaning gases are thenexhausted from chamber 15 with the exhaust system discussed above. Thecleaning process of chamber 15 and the cleaning of wafer surfaces arediscussed in detail below.

F. Endpoint Detection System

FIGS. 17A-17D illustrate a cleaning endpoint detection system 800 formicrowave plasma system 55 according to another aspect of the presentinvention. As discussed above, apparatus 10 preferably employs a thermalcleaning technique using remote microwave technology, instead of aconventional in situ plasma process, to lower metal contamination. Inthe present invention, the gentle cleaning technique using remotemicrowave plasma system 55 utilizes only chemical reactions, in contrastto using in situ plasma processes where physical sputtering effects mayreact with the aluminum in the chamber walls and lead to aluminum metalcontamination in the processed wafer.

In the cleaning process using remote plasma system 55, the plasma isproduced remotely from chamber 15 such that the etchant gas, preferablymostly of fluorine radicals, is directed into the chamber where thegentle thermal clean occurs, but the plasma remains exterior to thechamber (i.e., within applicator tube 292, see FIG. 16). While thisprocess has a number of advantages for cleaning a wafer in chamber 15and/or components of chamber 15 (discussed above), the lack of plasma inthe chamber can make it difficult, using conventional endpoint detectionsystems, to pinpoint the time at which the cleaning has been completed,i.e., when the last process gas residue in the chamber has reacted withthe cleaning etchant so that it can be discharged from the chamber.Conventional endpoint detection systems typically rely on the use of aplasma within the chamber and check emissions from the in situ plasma todetermine the end of a cleaning process.

The endpoint detection system of the present invention, however, may beused with either an in situ plasma or a remote plasma, such as providedby microwave plasma system 55. For example, in one exemplary process,fluorine-based gas is used to react with SiO₂ powder residue in thechamber to form a SiF₄ gas, which is drawn out of chamber 15 with thevacuum pump. When substantially all of the SiO₂ in the chamber has beenconsumed, the fluorine-based gas cannot react with the SiO₂ to formSiF₄. Instead, the fluorine-based gas may begin to contaminate thechamber 15 or to react with, for example, the aluminum walls of thechamber to form an aluminum fluoride compound. Consequently, it isimportant to determine the approximate endpoint or the point at whichthe last SiO₂ residue has reacted with the fluorine gas so that gatevalve 280 can be closed to prevent further fluorine radicals fromentering chamber 15. As discussed further below, endpoint detectionsystem 800 of the present invention determines the endpoint of acleaning process by detecting changes in light intensity that occur dueto absorbance of light by the exhausted clean gas reactants such asSiF₄.

As shown in FIG. 17A, cleaning endpoint detection system 800 includes agas detector 802 positioned along discharge conduit 60 between isolationvalve 371 and throttle valve 373. Of course, gas detector 802 may bepositioned in other locations within the exhaust system of apparatus 10.For example, detector 802 may be positioned downstream of throttle valve373, as shown in FIG. 17B. In another embodiment, detector 802 ispositioned along a bypass line 804 that receives a sample stream of gasfrom conduit 60, as shown in FIG. 17C. In this embodiment, bypass line804 may include a control valve 806 to vary the amount of flow passingthrough line 804, or to completely cease gas flow along bypass line 804,for example, during gas processing of a wafer within the chamber.

Referring to FIG. 17D, a preferred embodiment of gas detector 802 willnow be described. As shown, detector 802 includes a housing 804 defininga through-hole 806 in communication with conduit 60 for allowing thegases and other residue from chamber 15 to pass therethrough. A pair offlanges 808, 810 preferably attach housing 804 to conduit 60. The sidewalls of housing 804 include a pair of infrared (IR) windows 812, 813that are configured to allow far-IR light to pass through. Far-IR lighthas wavelength starting at about 10 μm. IR windows 812, 813 are spacedby a length L and preferably comprise a material substantiallytransparent to far-IR light such that zero or substantially little ofthe light is absorbed by windows 812, 813. In addition, the IR window812, 813 material should be process-compatible, inert with respect tothe process and clean gas chemistry, and the material should notcontaminate the film. In embodiments where fluorine radicals are usedfor the cleaning process, windows 812 and 813 are resistant to fluorine.Preferred materials for IR windows 812, 813 include germanium, calciumfluoride, or the like.

As schematically shown in FIG. 17D, detector 802 further includes afar-IR lamp 814 suitably coupled to housing 804 for generating far-IRlight and transmitting this light through windows 812, 813 so that thelight passes through-hole 806. An IR detector 816 is coupled to housing804 in position to receive and detect the far-IR light passing throughwindow 813. Preferably, far-IR lamp 814 may be a tungsten lamp sourcewith an optical notch filter.

When the present invention is in use, the clean gas reactants (e.g.,SiF₄) are directed along conduit 60 and through-hole 806 of detector802. Far-IR lamp 814 transmits far-IR light through window 812,through-hole 806 and window 813, where it is received by detector 816.As the light passes through the clean gas SiF₄ reactants, thesereactants (i.e., the silicon) absorb a portion of the far-IR light,which reduces the light intensity received by detector 816. The fluorinedoes not absorb the far-IR light. Therefore, when the far-IR lightintensity detected increases up to a reference value, detector 816 sendsa signal to a controller (not shown) indicating that the concentrationof SiF₄ passing through conduit 60 has substantially diminished orcompletely stopped, which indicates that the cleaning endpoint hasarrived. At this point, the controller sends an appropriate signal toprocessor 50 to close gate valve 280 and to prevent further etchant gasfrom entering chamber. In the above exemplary clean process, endpointdetection system 880 utilizes source 814 to provide, and detector 816 todetect, far-IR wavelengths that can be absorbed by clean gas reactantsSiF₄, which absorb light with a wavelength of about 10 μm, and fluorine,which absorbs light with a wavelength of about 5-6 μm. In otherembodiments, source 814 and detector 816 can provide light at differentwavelengths, depending on the light absorbance characteristics of thespecific clean gas reactants utilized in the clean gas process.

By way of example, I₀ is the intensity of the far-IR light when no SiF₄is flowing through conduit 60 and the detector 816 receives the fullintensity from lamp 814. As SiF₄ flows through through-hole 806 duringcleaning, the far-IR light is absorbed and the intensity received bydetector 816 (I) is reduced, given by the expression:

    I/I.sub.0 =exp(-X*L*C)

where X is the extinction coefficient of IR windows 812, 813 or a filter(not shown), L is the length between windows 812, 813 (see FIG. 17D) andC is the concentration of SiF₄ passing through detector 802. As I/I₀approaches the value 1, the SiF₄ concentration is diminishing, whichmeans that the cleaning endpoint is approaching. The controllercontinuously monitors I/I₀ until this value approaches 1, whichindicates that the cleaning endpoint has arrived.

While the description above is in terms of a CVD chamber for amultichamber processing system, it would be possible to implementcertain features of the present invention with other plasma etchingchambers, physical deposition chambers or the like. Therefore, the abovedescription and illustrations should not be taken as limiting the scopeof the present invention as defined by the appended claims. It should benoted that the invention is not limited to a single wafer chamber asdescribed above and shown in the enclosed drawings. For example, thethrottle valve of the present invention could be installed into a batchchamber that simultaneously processes a plurality of wafers. Inaddition, the invention would be suitable for use in a multiple waferchamber that sequentially performs individual processing steps on eachof the wafers.

II. High Temperature Multiple-Step Processes Using the CVD ReactorSystem

A. Exemplary Structures and Applications

FIG. 18 illustrates a simplified cross-sectional view of an integratedcircuit 900 according to the present invention. As shown, integratedcircuit 900 includes NMOS and PMOS transistors 903 and 906, which areseparated and electrically isolated from each other by a field oxideregion 920 formed by local oxidation of silicon (LOCOS), or othertechnique. Alternatively, transistors 903 and 906 may be separated andelectrically isolated from each other by a shallow trench isolation (notshown) when transistors 903 and 906 are both NMOS or both PMOS. Eachtransistor 903 and 906 comprises a source region 912, a drain region 915and a gate region 918.

A premetal dielectric (PMD) layer 921 separates transistors 903 and 906from metal layer 940 with connections between metal layer 940 and thetransistors made by contacts 924. Metal layer 940 is one of four metallayers 940, 942, 944, and 946, included in integrated circuit 900. Eachmetal layer 940, 942, 944, and 946 is separated from adjacent metallayers by respective inter-metal dielectric layers 927, 928, and 929.Adjacent metal layers are connected at selected openings by vias 926.Deposited over metal layer 946 are planarized passivation layers 930.CVD apparatus 10 may be used to deposit films used, for example, as PMDlayer 921, IMD layers 927, 928 and 929, or passivation layer 930. CVDapparatus 10 also may be used to deposit oxide filling layers forshallow trench isolation structures used in place of LOCOS field oxideregion 920.

Another example of a use of CVD apparatus 10 described above is formingultra-shallow source and drain regions 912 and 915 shown in exemplaryintegrated circuit 900 of FIG. 18. Application of the present method forforming ultra-shallow doped junctions in forming the source/drainregions for a MOS transistor is discussed, as an example, with FIGS.19A-19E.

FIG. 19A is a simplified cross-sectional view of a partially completedMOS transistor. Merely as an example, the MOS transistor 1000 is a PMOStransistor. Of course, NMOS transistors also may be formed. For PMOStransistor 1000, a doped dielectric layer 1008 used may be a BSG film asthe P type dopant source. As seen in FIG. 19A, a gate electrode 1002overlying gate oxide 1003 has already been formed on material 1004. Inthe present example, material 1004 may be an N type substrate or an Nwell formed in a substrate. Field oxide regions 1006 also have beenformed by a method such as local oxidation of silicon (LOCOS). Theregions where ultra-shallow doped junctions are desired may be definedusing a mask. In the present example, the regions are source/drainregions 1010 and 1012, but of course the regions may be defined to formlightly doped drain (LDD) regions. Using the CVD reactor systemdescribed above with process recipes discussed in detail below, a dopeddielectric layer 1008 is formed over source/drain regions 1010 and 1012on a wafer resting on resistively-heated heater 25.

Prior to forming doped dielectric layer 1008 over source/drain regions1010 and 1012, the surface of source/drain regions 1010 and 1012 may becleaned of any gate oxide or native oxide that may exist either by usinga plasma formed by reactive gases such as NF₃ from remote microwaveplasma system 55 described above or by using a thermal NF₃ vapor. Duringthe cleaning procedure, gate valve 280 would be opened to allow fluorineradicals from the NF₃ plasma to enter chamber 15 to clean the oxidesthat may exist on the surface of source/drain regions 1010 and 1012.Cleaning these oxides allows a more consistent drive-in of dopants fromdoped dielectric layer 1008 that is formed over source/drain regions1010 and 1012. The fluorine radicals from the remote plasma may be usedto clean native oxides from the wafer in chamber 15. In the cleaningprocedure, heater 25 may be adjusted to a position where the fluorineradicals are optimally able to clean the oxides without damaging thedevice on the wafer. Preferably, this native oxide removal/cleaning stepand the deposition of doped dielectric layer 1008 are performed in thesame chamber in an in situ manner. Use of the above described CVDapparatus 10 avoids moisture absorption by the wafer, since the vacuumof chamber 15 is not broken and the wafer is not exposed to theenvironment. Alternatively, undesired oxides may be cleaned from thewafer by thermally breaking down NF₃ vapor in situ. With thisalternative, fluorine radicals are produced in situ in chamber 15 byintroducing NF₃ between about 200-1500 standard cubic centimeters perminute (sccm), preferably about 500 sccm, and optionally O₂ at about0-1000 sccm into chamber 15. At the same time, chamber 15 is heated tobetween about 500-650° C., preferably 600° C., and maintained at apressure of between about 60-760 torr, preferably 400 torr, while heater25 is spaced between about 150-900 mil, preferably about 600 mil, fromplate 20. Thus, the surfaces of source/drain regions 1010 and 1012 canbe cleaned of any native oxide barrier.

After the cleaning step, gate valve 280 in some embodiments would beclosed to shut out any reactive gases used in the doped dielectric layerdeposition process from entering and depositing onto surfaces in conduit47. Heater 25 also would be moved into the appropriate processingposition and heated to the specified temperature in the vacuum ofchamber 15, according to the desired process recipe. Doped dielectriclayer 1008 is then formed at high temperatures (about 500-600° C.) inthe CVD apparatus 10, as described below. Without an native oxidebarrier, dopants from the doped dielectric layer 1008 formed on thewafer may more easily and uniformly be driven into the substrate to formultra-shallow source/drain regions 1010 and 1012.

After deposition of doped dielectric layer 1008, the wafer remains inchamber 15. The resistively-heated heater 25 and wafer thereon are thenheated to a higher temperature (about 800° C.) for a specified time. Theheating step drives dopants from doped dielectric layer into N typematerial 1004. Doped dielectric layer 1008 is used as a P type dopantdiffusion source for the resulting ultra-shallow junctions 1020, asshown in FIG. 19B. Of course, gate valve 280 remains closed during thisdrive-in step. As an alternative to being heated in situ, the wafer maybe transferred to an annealing furnace or a rapid thermal processreactor (preferably within the multichamber system) to drive-in dopantsfrom doped dielectric layer 1008, which acts as a dopant diffusionsource. Diffusion is performed by annealing or a rapid thermal process.Preferably, the diffusion is performed using a rapid thermal process(due to better throughput) at a temperature between about 950-1100° C.for between about 1-3 minutes, and preferably about 1000° C. for about 1minute, in these other embodiments.

After diffusion, doped dielectric layer 1008 is removed by dry or wetetching techniques or other removal technique from N type material 1004.CVD apparatus 10 may also be used to remove doped dielectric layer 1008by using remote microwave plasma system 55 with the appropriate etchingchemistry. For this dielectric removal step, gate valve 280 would beopened to allow the remote plasma to etch the layer 1008 until removalis completed, whereupon gate valve 280 is closed. The removal step maybe performed in situ without transferring the wafer from heater 25 inchamber 15. Alternatively, the removal step may be performed in anotherchamber, dedicated to dielectric removal, within the same multichambersystem as CVD apparatus 10, which also avoids exposure of the wafer tothe environment outside the vacuum of the multichamber system. FIG. 19Cillustrates the partially completed PMOS transistor 1000 after removalof doped dielectric layer 1008. PMOS transistor 1000 includes gateelectrode 1002 and adjacent source/drain regions 1020 which areultra-shallow P type doped junctions. Thereafter, remaining processsteps for the completion of the device may be performed on the wafer.

After every wafer (or several wafers) have been processed in chamber 15of CVD apparatus 10, a chamber clean may be performed. After processingof the wafer is completed within chamber 15, the wafer is transferredthrough slot 243 which is then vacuum locked. Gate valve 280 may then beopened to allow the chamber clean process to be performed using removemicrowave plasma system 55 until the chamber is cleaned tospecifications, as indicated by the endpoint detector system.

In an alternative embodiment, steps shown in FIGS. 19D-19E are performedafter steps described for FIG. 19A. After doped dielectric layer 1008 isformed over source/drain regions 1010 and 1012 and gate electrode 1002as seen in FIG. 19A, a capping layer 1030 such as USG is formedoverlying doped dielectric layer 1008, preferably in an in situ processwithin chamber 15. During the deposition of layer 1008, gate valve 280would remain closed. Then the substrate may be heated for diffusion ofdopants from doped dielectric layer 1008 into semiconductor material1004 as discussed above for FIG. 19B. Alternatively, the wafer may beremoved from chamber 15 for transfer to an annealing furnace or rapidthermal process reactor for diffusion of dopants from doped dielectriclayer 1008 as discussed above for FIG. 19B. Preferably, the substrateundergoes a rapid thermal process in the same multichamber system towhich chamber 15 (where doped dielectric layer 1008 and capping layer1030 were deposited) is a part. As seen in FIG. 19E, dopants from thedoped dielectric layer 1008 with overlying cap layer 1030 have diffusedinto semiconductor material 1004 to form ultra-shallow source and drainjunctions 1020. The cap layer 1030 and doped dielectric layer 1008 arethen etched away as discussed above to provide partially completed PMOStransistor 1000, as shown in FIG. 19C, ready for remaining processingsteps. For about a 0.25 μm device geometry, diffusion of boron atomsform a BSG film thickness between about 100-200 Å capped with a USG filmof between about 100-200 Å and results in a junction depth ranging frombetween about 0.05 μm to about 0.1 μm, according to preferredembodiments for PMOS transistors.

Of course, an NMOS transistor 1000 includes gate electrode 1002 andsource/drain regions 1010 and 1012 where N type, ultra-shallow junctionsmay be formed in the P type semiconductor material 1004 using a dopeddielectric film 1008 such as a PSG film or an arsenic-doped silicateglass film as the dopant source, according to other embodiments of thepresent invention. P type material 1004 may be a P type substrate or a Pwell formed in a substrate. For about a 0.25 μm device geometry, a PSGfilm thickness between about 100-200 Å and a USG film between about100-200 Å results in a depth of phosphorus driven into the semiconductormaterial that ranges from between about 0.05 μm to about 0.1 μm,according to preferred embodiments. Of course, it is recognized thatother doped silicate glass films may be used to provide the N type or Ptype ultra-shallow junctions depending on the application.

Another example of a use of the present invention is forming anultra-shallow doped region as a channel-stop in a shallow trenchisolation structure between devices. Application of the present methodfor forming an ultra-shallow channel-stop region is discussed withreference to FIGS. 20A-20G.

FIG. 20A is a simplified cross-sectional view of a partially completedshallow trench isolation structure formed in semiconductor material1100. As seen in FIG. 20A, a trench 1102 is formed in semiconductormaterial 1100 using anisotropic etching techniques including reactiveion etching, plasma etching, or other techniques. In the presentexample, the semiconductor material 1100 may be a P type substrate or aP well formed in a substrate. A mask 1104 may be used to define thechannel stop region in the shallow trench isolation. Using processrecipes discussed in detail below, a doped dielectric layer 1106 isformed over trench 1102 using mask 1104. Doped dielectric layer 1106provides a source of dopant atoms to diffuse and form a channel-stopdoping region used to prevent a conducting path from forming betweendevices in semiconductor material 1100. For P type material 1100, dopeddielectric layer 1106 may be a BSG film as the P type dopant source.

Prior to forming doped dielectric layer 1106 over trench 1102, thesurface of trench 1102 may be cleaned of any gate oxide or native oxidethat may exist by using remote microwave plasma system 55 to provide afluorine radicals in a remote plasma formed using reactive gases such asNF₃, as discussed below. During the cleaning step, gate valve 280 isopen to allow fluorine radicals to flow from conduit 47 through outerannular passage 297 and into chamber 15 via distribution plate 20.Heater 25 with the wafer thereon is lowered into a position for thecleaning so that the fluorine radicals can clear the wafer of theunwanted oxides that may exist on the surface of trench 1102 withoutdamaging the substrate. Cleaning these oxides allows a more consistentdrive-in of dopants from doped dielectric layer 1106 that is formed overtrench 1102. The cleaning step and the deposition of doped dielectriclayer 1106 are performed in chamber 15 in an in situ process. Inalternative embodiments, the cleaning step may be done by thermallybreaking down NF₃ in situ, as discussed above. The fluorine radicalsfrom the NF₃ plasma or vapor then clear the oxides that may exist on thesurface of trench 1102. In further alternative embodiments, a separatechamber of the multichamber system described above may be used for thiscleaning step. Since moisture absorption by the wafer is avoided by notbreaking the vacuum of chamber 15 (or alternatively of the multichambersystem), the surface of trench 1102 is free of native oxide barriers.After the cleaning step is performed, gate valve 280 is closed. Withoutthe native oxide barrier, dopants from doped dielectric layer 1106 maymore easily and uniformly be driven into the substrate to formultra-shallow junctions used as a channel-stop region to provide shallowtrench isolation. Heater 25 with the wafer thereon is moved into theprocessing position and heated to high temperatures (about 500-700° C.)for deposition of layer 1106.

After deposition of doped dielectric layer 1106, the wafer remains inchamber 15 for the drive-in step. Gate valve 280 remains closed, andheater 25 is heated to a higher temperature (about 800° C.). The heatingoccurs for a specified time that depends on the desired junction depthneeded for the diffusion. Alternatively, the wafer may then betransferred to an annealing furnace or a rapid thermal process reactor(preferably within the multichamber system) to drive dopants from dopeddielectric layer into P type material 1100. Doped dielectric layer 1106is used as a P type dopant diffusion source for the resultingultra-shallow channel-stop region 1108, as shown in FIG. 20B.Ultra-shallow channel-stop region 1108 is a P+ type region formed in Ptype material 1100.

After diffusion, doped dielectric layer 1106 is removed by wet etchingtechniques or other removal technique from P type material 1100.Preferably, the wafer remains in chamber 15 so that gate valve 280 maybe opened and radicals from remote microwave plasma system 55 may etchaway layer 1106. Of course, reactive gases input to plasma system 55depend on the type of doped dielectric layer 1106. FIG. 20C illustratesthe partially completed shallow trench isolation structure after removalof doped dielectric layer 1106. As seen in FIG. 20D, trench 1102 is thenfilled with an oxide 1110 to form the shallow trench isolationstructure. In a preferred embodiment, a high quality USG film depositedat high temperature may be used as oxide 1110 to fill high aspect ratiotrenches. Oxide 1110 also may be formed using other depositiontechniques.

After completing shallow trench isolation structure having ultra-shallowchannel-stop region 1108, devices 1112 and 1114 separated by shallowtrench isolation structure may be formed, as seen in FIG. 20E. Devices1112 and 1114 each include a gate electrode 1116 and adjacentsource/drain regions 1118 and 1120. Thereafter, remaining process stepsfor the completion of the device may be performed by transferring thewafer to another chamber, preferably in multichamber system. After thewafer is transferred from chamber 15, a chamber clean may be performedusing remote microwave plasma system 55 with resistively-heated heater25 adjusted to a cleaning position and gate valve 280 being open, asalready described above in connection with FIGS. 19A-19E.

In an alternative embodiment, steps shown in FIGS. 20F-20G are performedafter steps shown in FIG. 20A. After doped dielectric layer 1106 isformed over trench 1102 and mask 1104 as seen in FIG. 20A, a cappinglayer 1110 such as USG is formed overlying doped dielectric layer 1106in chamber 15 in an in situ process. During the deposition of cappinglayer 1110, gate valve 280 is closed. Then the substrate is heated insitu in chamber 15 for dopant drive-in for diffusion of dopants fromcapped, doped dielectric layer 1106 into semiconductor material 1100 asdiscussed above for FIG. 20B. Alternatively, the wafer may be removedfrom chamber 15 for transfer to an annealing furnace or rapid thermalprocess reactor (preferably within the multichamber system) fordiffusion of dopants from capped, doped dielectric layer 1106 intosemiconductor material 1100 as discussed above for FIG. 20B. As seen inFIG. 20G, dopants from the doped dielectric layer 1106 with overlyingcap layer 1110 have diffused into semiconductor material 1100 to formultra-shallow channel-stop region 1108. Cap layer 1110 minimizes theoutgassing of dopants upward from doped dielectric layer 1106, therebyresulting in more dopants diffusing down into the substrate material1100. After the diffusion step is performed, gate valve 280 is openedand both the cap layer 1110 and doped dielectric layer 1106 may thenetched away using remote microwave plasma system 55 with appropriateetchant chemistry to provide partially completed shallow trenchisolation as shown in FIG. 20C, ready for the remaining processing stepsof FIGS. 20D-20E. When the wafer is transferred out of chamber 15, gatevalve 280 is in the closed position. A chamber clean of chamber 15 canthen be performed by operating the plasma system 55 with gate valve 280opened.

For shallow trench isolation between NMOS transistors in a P typesubstrate, the doped dielectric film 1106 may be a BSG film. For shallowtrench isolation between PMOS transistors in an N type substrate (or inN wells of CMOS circuits), the doped dielectric film 1106 may be a PSGfilm or an arsenic-doped silicate glass film. For smaller devicegeometries such as less than 0.35 μm having a trench 1102 with a depthof about 0.5 μm, channel stop region 1108 of about 0.1 μm junction depthmay be formed using a BSG film 1106 about 200 Å thick and a USG cappingabout 200 Å thick, according to preferred embodiments of the presentinvention.

It should be understood that simplified integrated circuit 900 is forillustrative purposes only. One of ordinary skill in the art couldimplement the present method for fabrication of other integratedcircuits such as microprocessors, application specific integratedcircuits (ASICS), memory devices, and the like. Further, the presentinvention may be applied to PMOS, NMOS, CMOS, bipolar, or BiCMOSdevices. Although ultra-shallow source/drain junctions and ultra-shallowtrench isolation applications are discussed above, the present inventionalso may be used in other applications where an ultra-shallow dopedregion is desired. The present invention also may be used for formingundoped oxides as well as doped oxides for use as various layers inintegrated circuit devices, including PMD, IMD, passivation, anddamascene layers.

Exemplary wafer cleaning, deposition, and chamber cleaning processes forin situ or individual operation within chamber 15 are further describedbelow, in accordance to various embodiments of the present invention.

B. Cleaning Native Oxides Prior to Deposition

In accordance with a specific embodiment of the present invention,native oxides that may exist on the silicon substrate or region where anultra-shallow doped junction is desired may be cleaned prior todeposition of the doped dielectric layer that may be used, for example,as a dopant diffusion source or as a PMD layer. In these embodiments,the native oxides can be cleaned by using fluorine radicals from aplasma formed with reactive clean gases like NF₃ by remote microwaveplasma system 55. Use of in situ processes in one chamber or alternatelyin chambers of the same multichamber system permit enhanced quality inthe ultra-shallow junctions formed in accordance with these specificembodiments, as well as providing for dielectric layers having lowmoisture content and low shrinkage.

In a specific embodiment, chamber 15 is maintained at the depositiontemperature, a temperature ranging between about 300-650° C., andpreferably at about 550-600° C., for the entire cleaning process.Chamber 15 is maintained at a pressure ranging between about 1-2 torr,preferably at about 1.5 torr, while maintaining the temperature. Heater25 is moved to a position about 600 mil from gas distribution plate 20,while gate valve 280 is opened and the clean gas NF₃ is introduced intoapplicator tube 292 at a rate of about 600 sccm. The clean gas isintroduced into applicator tube 292 and the pressure is permitted tostabilize for about 3 seconds before microwave energy is applied to theNF₃ in applicator tube 292. Microwave power of between about 500-2500Watts, preferably between about 1000-1500 Watts, from magnetron 711operating in CW mode is then applied for about 5-10 seconds. Themicrowaves are transmitted from magnetron 711 through the waveguide andoptimizing system to enter applicator tube 292 through the window, asdiscussed above. UV lamp 731 ignites the reactive gases in applicatortube 292 to form a plasma, with ionization sustained by the microwaveenergy entering applicator tube 292 at the window. The radicals from theupstream plasma formed in applicator tube 292 are output to flow intoinlet 290. The radicals flow through the lined passage in enclosureassembly 200 to conduit 47 of clean manifold 270 through the opened gatevalve 280 and into outer annular passage 297 to enter chamber 15 andclean native oxides off the wafer. Used clean gas reactants and oxideresidues are then exhausted out of chamber 15 via the opened throttlevalve. The present description is for chamber 15 which has a totalvolume of about 6 liters. It is recognized that flow values may differdepending on the size and type of chamber used in other embodiments.

In a specific embodiment, with chamber 15 maintained at pressures lowerthan about 1-2 torr, rapid removal of fluorine species occurred,resulting in poor cleaning results. At chamber pressures higher thanabout 1-2 torr, recombination may occur due to collision losses, as wellas causing overheating and damage to applicator tube 292. Chamber 15should be maintained at pressure levels where fluorine species are notrapidly removed, recombination does not occur, and applicator tube 292does not break. In some embodiments, the chamber pressure may be limitedby the physical dimensions and material of applicator tube 292, whenmicrowave power is being applied. In a specific embodiment, the pressurein applicator tube 292, when microwave power is applied, may be about 3times as much as the optimal chamber pressure. When different applicatortubes are used with different flow rates, the optimal chamber pressurewill vary. Of course, any pressure may be used when applicator tube 292is used without microwaves being applied.

Since the plasma is formed upstream of the wafer, only the reactivefluorine radicals in the plasma are able to reach the wafer to clean thenative oxides from the wafer. As mentioned above, the cleaning steppreferably is done for about 5-10 seconds for a typical native oxide ofthickness of about 90 Å. The above cleaning step etches native oxides ata rate of about 2 μm/minute. Of course, the total time of the cleaningstep depends on the thickness of the particular oxide to be cleared offthe wafer. With remote microwave plasma system 55 of present invention,native oxides or other oxides may be etched and plasma damage to thewafer is avoided.

Although the above wafer cleaning process conditions are exemplary forthe present embodiment, other conditions may also be used. The abovedescription discusses NF₃, merely as an example, in a Giga Fill™ Centurasystem available from Applied Materials fitted for 200-mm wafers, as dothe various deposition descriptions below. However, otherfluorine-containing or chlorine-containing gases, such as NF₃ and N₂,NF₃ and argon, NF₃ and O₂, a dilute F₂, CF₄, C₂ F₆, C₃ F₈, SF₆ or Cl₂,etc., may be used as well.

C. Exemplary Silicate Glass Depositions

According to the process of the present invention, dielectric layersused as the dopant source, PMD layer, IMD layer, oxide filling layer,capping layer, or other layers may be formed using any of severaldifferent processes. The process recipes of a BSG film, a PSG films, aBPSG film, and a USG film are set forth below as examples of doped andundoped dielectric layers used in the present invention. Of course,during the below described deposition of various dielectric films, gatevalve 280 remains closed (unless remote plasma system 55 is being usedfor deposition, in accordance with an alternative embodiment). Theexemplary processes may be performed in CVD apparatus 10, which is aclosed, single-wafer, SACVD system in preferred embodiments.

CVD apparatus 10 also may be adapted with different and/or additionalinput gas supply sources to deposit BPSG, arsenic doped silicate glass(AsSG), or other dielectric layers as well. Of course, those of ordinaryskill in the art will understand that other process recipes and otherreaction systems like plasma enhanced CVD (PECVD) may also be used todeposit the dielectric films. Examples of boron sources include TEB,trimethylborate (TMB), diborane (B₂ H₆), and other similar compounds.Examples of phosphorus sources include triethylphosphate (TEPO),triethylphosphite (TEP_(i)), trimethylphosphate (TMOP),trimethylphosphite (TMP_(i)), and other similar compounds. In additionto BSG or PSG films, arsenic doped oxides or arsenic silicate glass(AsSG) also may be deposited using, for example, a liquid source with anarsenic compound or an arsenic gas diluted in argon, as examples.Examples of silicon sources include silane (SiH₄), TEOS, or a similarsilicon source, and oxygen sources include O₂, O₃, microwave-generatedatomic oxygen (O), or the like. In the descriptions below, flow ratesfor liquid sources are provided in milligrams per minute (mgm) while gasflow rates are provided in standard cubic centimeters per minute (sccm).In these descriptions, liquid sources are vaporized using a PrecisionLiquid Injection System, and liquid flow rates in mgm may be convertedto gas flow rates in sccm by multiplying liquid flow rates by a factorof about 1.923 so that flow ratios may be calculated accordingly.Preferably, stable doped dielectric films may be formed using theTEOS/O₃ chemistry in a SACVD process to form damage-free, uniformlydoped ultra-shallow junctions in some embodiments. In other embodiments,a low moisture doped dielectric film may be formed using TEOS/O₃chemistry with a SACVD process conducted in CVD apparatus 10 to providea planarized insulating layer with high aspect ratio gap-fill, lowshrinkage, low metal contamination, and low fluorine incorporation.

1. Exemplary BSG Film Deposition

As merely an example, the BSG film deposition recipe described below iscapable of forming a BSG film that may be useful as a doped dielectriclayer used as a dopant diffusion source. Of course, the recipe may bevaried depending on the particular use for and desired qualities of theBSG layer. A PSG layer formed as a doped dielectric layer used as adopant diffusion source could similarly be formed using the recipe belowand appropriately substituting the dopant source gas employed.

The exemplary BSG bulk film is deposited by heating the wafer and heater25 to a temperature of between about 200-650° C., preferably to atemperature within the range of about 400-650° C. and most preferably toabout 500° C., and maintaining this temperature range throughout thedeposition. With gate valve 280 closed, chamber 15 is maintained at apressure within a range of about 10-760 torr. Preferably, the pressureis maintained within the range of about 400-600 torr, and mostpreferably it is maintained at about 600 torr. Heater 25 is positionedabout 150-300 mil from gas distribution plate 20 and is preferablypositioned about 250 mil from plate 20.

A process gas including TEB as the source of boron, TEOS as the sourceof silicon, and O₃ as a gaseous source of oxygen is formed. Beingliquids, the TEB and TEOS sources are vaporized and then combined withan inert carrier gas such as helium. The liquids are vaporized either byliquid injection system in gas mixing system 93, which provides greatercontrol of the volume of reactant liquid introduced. The flow rate ofTEB is between about 50-550 mgm depending on the desired dopantconcentrations, while the TEOS flow rate is between about 300-1000 mgmand preferably about 500 mgm. The vaporized TEOS and TEB gases then aremixed with a helium carrier gas flowing at a rate of between 3000-6000sccm, preferably at a rate of about 4000 sccm. Oxygen in the form of O₃is introduced at a flow rate of between about 3000-6000 sccm and ispreferably introduced at a flow rate of about 5000 sccm. The ozonemixture contains between about 5-16 weight percentage (wt %) oxygen. Thegas mixture is introduced into chamber 15 from the distribution plate 20to supply reactive gases to the substrate surface where heat-inducedchemical reactions take place to produce the desired film.

The above conditions can result in a BSG film deposited at a rate ofbetween 500-1000 Å/minute. By controlling the deposition time, BSG filmshaving a thickness between about 50-500 Å and preferably between about100-300 Å may be formed at the process conditions described above inabout 10-60 seconds. The thickness of the BSG film deposited may thus beeasily controlled. Preferably, the wt % of boron in the resulting BSGfilm ranges between about 2-8 wt % and preferably is about 6 wt %.

2. Exemplary PSG Film Deposition

As merely an example, the PSG film deposition recipe described below iscapable of forming a PSG film that may be useful as a PMD layer. Ofcourse, the recipe may be varied depending on the particular use for anddesired qualities of the PSG layer. Other doped dielectric layersbesides PSG films may used as PMD layers by using similar recipes to therecipe below and appropriately substituting the dopant(s) source gas(es)employed.

The exemplary PSG bulk film is deposited by heating the wafer and heater25 to a temperature of between about 200-650° C., preferably to atemperature within the range of about 400-650° C. and most preferably toabout 600° C., and maintaining this temperature range throughout thedeposition. With gate valve 280 closed, chamber 15 is maintained at apressure within a range of about 10-760 torr. Preferably, the pressureis maintained within the range of about 400-600 torr, and mostpreferably it is maintained at about 450 torr. Heater 15 is positionedabout 250-350 mil from gas distribution plate 20 and is preferablypositioned about 330 mil from plate 20.

A process gas including TEPO as the source of phosphorus, TEOS as thesource of silicon, and O₃ as a gaseous source of oxygen is formed. Beingliquids, the TEPO and TEOS sources are vaporized by the liquid injectionsystem and then combined with an inert carrier gas such as helium. Theflow rate of TEPO is between about 10-100 mgm, preferably between about5-30 mgm, most preferably about 24 mgm, depending on the desired dopantconcentration, while the TEOS flow rate is between about 500-1500 mgm,preferably about 1000 mgm. The vaporized TEOS and TEPO gases then aremixed with a helium carrier gas flowing at a rate of between 2000-6000sccm, preferably at a rate of about 4000 sccm. Oxygen in the form of O₃(having between about 5-16 wt % oxygen) is introduced at a flow rate ofbetween about 2500-6000 sccm and is preferably introduced at a flow rateof about 4000 sccm. The gas mixture is introduced into chamber 15 fromgas distribution plate 20 to supply reactive gases to the substratesurface where heat-induced chemical reactions take place to produce thedesired film.

The above conditions result in a PSG film deposited at a rate of about1780 Å/minute. By controlling the deposition time, the thickness of thePSG film deposited may thus be easily controlled. Preferably, the wt %of phosphorus in the resulting PSG film ranges between about 2-8 wt %and preferably is about 4 wt %.

3. Exemplary BPSG Film Deposition

As merely an example, the BPSG film deposition recipe described below iscapable of forming a BPSG film that may be useful as a PMD layer. Ofcourse, the recipe may be varied depending on the particular use for anddesired qualities of the BPSG layer.

The exemplary BPSG bulk film is deposited by heating the wafer andheater 25 to a temperature of between about 100-800° C., preferably to atemperature within the range of about 400-650° C. and most preferably toabout 480° C., and maintaining this temperature range throughout thedeposition. With gate valve 280 closed, chamber 15 is maintained at apressure within a range of about 10-760 torr. Preferably, the pressureis maintained within the range of about 150-600 torr, and mostpreferably it is maintained at about 200 torr. Heater 15 is positionedabout 150-400 mil from gas distribution plate 20 and is preferablypositioned about 300 mil from plate 20.

A process gas including TEB as the source of boron, TEPO as the sourceof phosphorus, TEOS as the source of silicon, and O₃ as a gaseous sourceof oxygen is formed. Being liquids, the TEB, TEPO and TEOS sources arevaporized by the liquid injection system and then combined with an inertcarrier gas such as helium. Of course, it is recognized that othersources of boron, phosphorus, silicon, and oxygen also may be used. Theflow rate of TEB is preferably between about 150-200 mgm. The flow rateof TEPO is between about 10-100 mgm, preferably between about 35-75 mgm,most preferably about 24 mgm, depending on the desired dopantconcentration, while the TEOS flow rate is between about 300-700 mgm.The vaporized TEOS, TEB, and TEPO gases then are mixed with a heliumcarrier gas flowing at a rate of between 2000-8000 sccm, preferably at arate of about 6000 sccm. Oxygen in the form of O₃ is introduced at aflow rate of between about 2000-5000 sccm and is preferably introducedat a flow rate of about 4000 sccm. The ozone mixture contains betweenabout 5-16 wt % oxygen. The gas mixture is introduced into chamber 15from gas distribution plate 20 to supply reactive gases to the substratesurface where heat-induced chemical reactions take place to produce thedesired film.

The above conditions result in a BPSG film deposited at a rate ofbetween 3500-5500 Å/minute. By controlling the deposition time, thethickness of the BPSG film deposited may thus be easily controlled. Theresulting BPSG film has a boron concentration level of between 2-6 wt %and a phosphorus concentration level of between 2-9 wt %.

The parameters in the above BSG, PSG, BPSG processes and in the belowUSG processes should not be considered limiting to the claims. Forexample, the present invention is also applicable to silicon oxide filmsdoped with other dopants including, for example, arsenic. As anotherexample, the flow values discussed above apply for a chamber outfittedfor 200-mm wafers, but may differ depending on the type or size of thechamber used. One of ordinary skill in the art can also use otherchemicals, chamber parameters, and conditions to produce similar films.

It is believed that film stability may be a factor in the availabilityof dopant atoms in the doped dielectric films for diffusion into thesemiconductor material. Several methods to improve film stability andimprove the ability to control dopant diffusion from these dopeddielectric films into the semiconductor material were investigated. Eachmethod described may be performed on a doped dielectric layer, after thelayer is deposited using a recipe such as one of the exemplarydeposition recipes described above. Furthermore, although methodsdescribed below are with respect to treatment of a BSG (or PSG) film,the methods are equally applicable to any doped silicon oxide film.

4. Exemplary USG Film Depositions

a. Oxide Filling Material or Insulating Layer

According to one embodiment of the present invention, an undopedsilicate glass (USG) layer can be deposited in CVD apparatus 10 for use,for example, as an oxide filling material for filling a shallow trenchused for shallow trench isolation. Of course, the USG film also may beused as an IMD layer, an insulating layer, or other layer. The exemplaryUSG recipe discussed below provides a very dense and uniform film whichcan survive annealing at temperatures of greater than 800° C. withminimal shrinkage. The USG film, which provides excellent gap fillcapability for high aspect ratio step coverage, can also endure severaletch processes at very uniform etch rate without opening up any voids inthe USG. The USG film, also can endure chemical mechanical polishing(CMP) planarization without opening up any voids or creases in the USG.

The wafer and heater 25 are heated to a temperature within the range ofabout 200-650° C., but preferably between about 550-650° C., and thenmaintained at this temperature throughout the deposition. Heater 25 ispositioned about 250-400 mil away from gas distribution plate 20 andpreferably at about 350 mil. With gate valve 280 closed, the pressure inchamber 15 is maintained at a level of between about 10-760 torr,preferably about 600 torr.

A process gas comprising oxygen and silicon sources is introduced intothe deposition chamber. In a preferred embodiment, the silicon source isTEOS and the oxygen source is O₃, but those skilled in the art willrecognize that additional silicon sources such as SiH₄, TMCT or similarsources, and other oxygen sources such as O₂, H₂ O, N₂ O,microwave-generated atomic oxygen, and similar sources and mixtures ofthe same also can be employed. When TEOS is used as a silicon source, acarrier gas such as helium or nitrogen is employed. The ratio of O₃ toTEOS may range from about 2-17:1, but is preferably between about 2-6:1.

The optimal total flow of the gaseous reactants will vary according tothe geometry and design of the deposition chamber. The gas flow also canbe varied to control the deposition rate. Typically, TEOS is introducedat a flow rate of between about 500-2500 mgm and is preferablyintroduced at a flow rate of about 2000 mgm. O₃ (between about 5-16 wt %oxygen) is introduced at a flow rate of between about 2000-10000 sccm,preferably about 5000 sccm. Helium or nitrogen may be used as a carriergas that is introduced at a flow rate of between 2000-10000 sccm andpreferably about 7000 sccm. Usually, the total flow of gases into thedeposition chamber will vary between about 5000-20000 sccm, preferablyabout 15000 sccm. Under the above conditions, deposition rates of about1450 Å/minute or greater are attainable. The flow values above are for a200-mm wafer chamber and will vary depending on size of chamber used andsize of wafer.

b. Capping Layer

According to another embodiment of the present invention, the depositedBSG (or PSG) layer may be capped with a thin, separate USG layer. TheUSG capping layer is a stable film that does not readily absorbmoisture. Thus, the USG capping layer provides a hydrophobic surface ontop of the BSG (or PSG) layer that prevents moisture present in theambient from being absorbed into the BSG (or PSG) film. Furthermore, theUSG capping layer is a relatively dense film that impedes boron (orphosphorus) evolution. The USG capping layer thereby facilitatescontrolled diffusion of more dopant atoms in the doped dielectric layerdownward into the semiconductor material. Without the USG capping layer,some of the dopant atoms may diffuse upward away from the semiconductormaterial during the subsequent anneal or rapid thermal process. Thus,the use of a capping layer contributes to controlling the diffusion andthe junction depth. The USG layer can be deposited in a separateprocessing chamber from the BSG (or PSG) layer, but preferably is doneas an in situ process in chamber 15 where deposition of the BSG (or PSG)layer also occurred. Of course, many processes for forming a cappinglayer are possible.

The following process for forming a USG layer is described as anexample. An undoped silicate glass layer may also be used not only as acapping layer, as described below, but as an insulating dielectric layerwithout use of an underlying doped dielectric layer.

The wafer and heater 25 are heated to a temperature within the range ofabout 200-600° C., but preferably about 500° C., and then maintained atthis temperature throughout the deposition. Heater 25 is positionedabout 250-350 mil away from gas distribution plate 20 and preferably atabout 300 mil. With gate valve 280 closed, the pressure in chamber 15 ismaintained at a level of between about 50-760 torr, and is preferably ata pressure of between about 200-600 torr, most preferably about 400torr.

A process gas comprising oxygen and silicon sources is introduced intothe deposition chamber. In a preferred embodiment, the silicon source isTEOS and the oxygen source is O₃, but those skilled in the art willrecognize that additional silicon sources such as silane, TMCT orsimilar sources, and other oxygen sources such as O₂, H₂ O, N₂ O andsimilar sources and mixtures of the same also can be employed. When TEOSis used as a silicon source, a carrier gas such as helium or nitrogen isemployed. The ratio of O₃ to TEOS may range from about 2-17:1, but ispreferably between about 2-6:1.

The optimal total flow of the gaseous reactants will vary according tothe geometry and design of the deposition chamber. The gas flow also canbe varied to control the deposition rate. Typically, TEOS is introducedat a flow rate of between about 500-1500 mgm and is preferablyintroduced at a flow rate of between about 1000-1250 mgm. O₃ (betweenabout 5-16 wt % oxygen) is introduced at a flow rate of between about2000-10000 sccm, preferably about 7000 sccm. Helium or nitrogen may beused as a carrier gas that is introduced at a flow rate of between2000-6000 sccm and preferably about 4000 sccm. Usually, the total flowof gases into the deposition chamber will vary between about 5000-20000sccm, preferably about 15000 sccm. Under the above conditions,deposition rates of between about 500 and 1500 Å/minute are attainable.At such deposition rates, a USG layer of about 100-200 Å can bedeposited in approximately 20 seconds. The flow values above are for a200-mm wafer chamber and will vary depending on size of chamber used andsize of wafer.

The following processes for forming a USG capping layer are described asexamples. Preferred applications will have USG cap layers of betweenabout 50-500 Å, and preferably between about 100 and 300 Å. A person ofordinary skill in the art, however, will realize that capping layers ofdifferent thickness can be employed depending on the specificapplication and device geometry size. Depending on the application andgap sizes in which the deposited film is used, it may be preferable,although not essential, that the capping and doped dielectric layers berelatively thin. For thin layers, the time to deposit and the time toetch away are reduced compared to thicker layers. The USG capping layeris deposited, and both the USG layer and the doped dielectric layer areetched back. It is also recognized that different capping layers such asother similar stable oxide films may be utilized to cap the dopeddielectric layer. Further, the USG cap layer may be formed over dopeddielectric films deposited by APCVD, PECVD, or LPCVD, in place of SACVD.As discussed above, use of chamber 15 for in situ performance ofmultiple process steps is most preferred, with use of a multichambersystem in which vacuum is not broken during transfer of substratesbetween various chambers in the multichamber system is also preferred.

According to another embodiment of the present invention, an in situ USGor similar cap layer is formed on a doped dielectric film by turning offthe boron source or the phosphorus source just before completion ofdeposition of the doped layer. In this embodiment, the initial dopeddielectric layer such as BSG (or PSG) is formed as described above. Flowof the dopant source into chamber 15 then is stopped while the thermalreaction continues for an additional period of between 1-30 seconds.Preferably, the thermal reaction continues for about 3-10 seconds. Inthis embodiment, the dopant source is stopped by closing a valve on thesource's supply line so that the thermal reaction is maintained withouta dopant for at least 5 seconds.

Of course, stopping the dopant gas source must be coordinated with thetime it takes the gas to travel from the point of the valve to the gasmixing system 93 and then through the faceplate of plate 20. In most CVDmachines several seconds is required for gas to flow from the injectionvalve to the deposition chamber, so the valve should be closedsufficiently in advance to allow for these delays. Thus, if TEB is theboron source, closing the valve on the TEB supply line several secondsbefore completion of deposition of the BSG layer results in a thin USGcap which prevents occurrence of the previously described moistureabsorption and outgassing phenomenon.

The in situ deposition of the USG cap formed on the doped dielectriclayer results in improved stability and immunity to moisture absorption,and contributes to improved control of the diffusion that formsultra-shallow doped regions.

Instead of or in addition to the use of a USG capping layer, a plasmatreatment of the doped dielectric layer also may be used to reducemoisture absorption and improve stability in the doped dielectric layer.In those embodiments equipped with a RF plasma system, this plasmadensification treatment may be used where plasma damage to the device isnot a significant concern. In some embodiments, the deposition attemperatures greater than about 500° C. may be sufficient to provide adense dielectric film. The improved stability of the plasmatreated dopeddielectric layer contributes to improved control of the diffusion thatforms the ultra-shallow doped regions. Chamber 15 is maintained atbetween about 1-5 torr during the plasma densification treatment. Withgate valve 280 closed, a plasma formed using a reactive gas such as, forexample, nitrogen (N₂), ammonia (NH₃), or argon, is introduced intochamber 15. As merely one example of the plasma treatment that may beused, a reactive gas such as N₂ is introduced in gas mixing system 93 ata rate of about 1000 sccm mixed with helium at 1000 sccm. RF plasmasystem is operated, for example, at a power level of about 450 Watts ata RF frequency of about 350 Megahertz (MHz) to create a plasma inchamber 15. The plasma serves to passivate the surface of the dopeddielectric layer, which may have some nitridation on its surface. Theplasma treatment thus densifies the doped dielectric film. More dopantsin the densified doped dielectric film, which is resistant to moistureabsorption, are available for forming the ultra-shallow junctions.

D. Heating Processes for In Situ Deposition and/or for Reflow

CVD apparatus 10 has high temperature capabilities allowing an in situheating step following a deposition process on the same wafer for atwo-step deposition/reflow process, or an in situ heating stepconcurrent to a deposition process on the same wafer for a one-stepdeposition/reflow process. For use as a PMD layer formed over highaspect ratio transistors or isolation trenches an undoped or dopeddielectric film, such as PSG, often requires planarization which isimportant in forming integrated circuit devices. Planarization of adoped dielectric layer may be performed by reflowing the layer at hightemperatures. Performing reflow also contributes to improving gap-fillof the deposited film, especially for high aspect ratio features on thewafer. Of course, heating steps for other purposes and applications alsomay be performed in CVD apparatus 10. The following heating procedurediscussed below serves merely as an exemplary heating step which may beused for reflow, but other heating steps for dopant drive-in in someapplications or for other purposes also can be done.

According to a specific embodiment, two-step deposition/reflow processis described below. With gate valve 280 closed, chamber 15 may bemaintained at a pressure of about 200-760 torr. With the wafer andheater 25 in the processing position between about 200-400 mil,preferably between about 330-350 mil, from distribution plate 20, thewafer and heater 25 are heated to a high temperature of between about500-800° C., preferably between about 550-650° C., in chamber 15, fordeposition processing. Stopping reactive gas flows, the wafer may thenbe heated at between about 750-950° C., preferably between about750-850° C. for about 5-30 minutes, preferably about 15-20 minutes, inorder to reflow the dielectric layer, according to a specificembodiment. The reflow temperature may be the same as or higher than thedeposition temperature in the two-step process. Further, for amultiple-step deposition/reflow process, the temperature may be rampedfrom the deposition temperature to an intermediate temperature (orintermediate temperatures) before being ramped to the reflowtemperature. Of course, the time and temperature for the heating stepsmay differ depending on the particular application being performed andon the particular layer being formed.

According to another specific embodiment, a one-step deposition/reflowprocess is described. With gate valve 280 closed, chamber 15 may bemaintained at a pressure of about 200-760 torr. With the wafer andheater 25 in the processing position between about 200-400 mil,preferably between about 330-350 mil, from distribution plate 20, thewafer and heater 25 are heated to a high enough temperature of betweenabout 750-950° C., preferably between about 750-850° C., in chamber 15,for simultaneous deposition and reflow processing to occur. Of course,the time and temperature for the deposition/reflow step may differdepending on the particular layer being formed.

As discussed above, keeping the wafer within the same chamber 15 formultiple in situ processes prevents exposure of the wafer to theenvironment, where moisture may be absorbed, and contamination byimpurities. Further, deposition of dielectric films at temperaturesgreater than about 550° C. can provide dense and high quality filmswhich do not form voids when heated. Deposition of the deposited filmsat these temperatures also reduces shrinkage.

E. Chamber Cleaning/Seasoning/Gettering Processes

After the processing step or multiple processing steps, such as theexemplary steps discussed above, have been performed on the wafer inchamber 15, the wafer is transferred out of chamber 15 for subsequentprocess steps as needed. When the vacuum lock door is closed, sealingchamber 15 without a wafer on heater 25, chamber 15 may undergo achamber cleaning process to eliminate deposition process residues suchas undesired oxides and/or nitrides from portions of chamber 15,including the unlined chamber walls in the lower portion of chamber 15,the bottom of heater 25, as well as other chamber components. To ensurereliable wafer-to-wafer repeatability, the chamber clean removes anyresidues built up during the deposition processes. These residues can becleaned from chamber components by using fluorine radicals, for example,from a plasma formed with reactive clean gases by remote microwaveplasma system 55. Due to its high reactivity with F atoms, residuesilicon oxide can be removed by the formation of a SiF₄ gas productwhich may be pumped away out of chamber 15. The chamber cleaningprocedure discussed below may be performed after processing of everywafer or every several wafers.

In a preferred embodiment of the present invention, NF₃ is used as theclean gas to provide the fluorine radicals. The present inventionpreferably uses remote microwave plasma system 55 to decompose NF₃ gasand generate a flow of F atoms into chamber 15. Using a fluorinechemistry with remote microwave plasma system 55 of the presentinvention advantageously has low kinetic energy and does not havephysical sputtering effects or formation of charging species in thesubsequently deposited film, compared to in situ plasma processes.Furthermore, consistent with environmental requirements to reduce globalwarming effects, the use of NF₃ does not generate any long-livedperflouro-carbon (PFC) products.

To ensure the best clean efficiency, the F flux as well as its cleaninguniformity should be optimized. At a certain NF₃ gas flow, there is athreshold microwave power setting, above which the generation of F atomsare compensated by their recombination. FIG. 21 shows the relationshipbetween NF₃ flow and microwave saturation power that gives the highestclean rate without any excessive hardware costs, in accordance with aspecific embodiment of the present invention. As shown in FIG. 21, themicrowave saturation power ranges from between about 1300-2100 Watts forcorresponding NF₃ flows of between about 500-950 sccm, according to thespecific embodiment. For a preferred embodiment discussed below, themicrowave saturation power is about 2100 Watts for a NF₃ flow of about950 sccm. The clean uniformity can be controlled by chamber pressure aswell as heater spacing, both of which can adjust the mean free path ofthe gas species and pumping profile. As discussed earlier, since thehighest pressure that can be tolerated by the above-discussed embodimentof applicator tube 292 is about 2 torr, spacing was used to optimizeclean uniformity. In other embodiments using different embodiments ofapplicator tube 292, both pressure and spacing may be used in the cleanuniformity optimization.

In an exemplary chamber cleaning process, chamber 15 is maintained at atemperature ranging between about 300-650° C., more preferably at about550-600° C. throughout the cleaning procedure, in preferred embodiments.Most preferably, chamber 15 is maintained at the same temperature atwhich the particular process is being run in chamber 15. For example,chamber clean processes would be run at 600° C. in those chambers used,as an example discussed above, for depositing PSG films at 600° C. Withthe throttle valve opened and gate valve 280 closed, heater 25 ispositioned about 100-250 mil, preferably about 150 mil, from gasdistribution plate 20 so that gas distribution plate 20 is heated up.Heating up gas distribution plate 20 allows a faster clean to occur.This heating step may be done for between about 3-10 seconds, preferablyabout 5 seconds.

Then, pressure and clean gas flow are optimally stabilized before theclean is performed. During the pre-clean stabilization step, chamber 15optimally should be maintained at pressure levels, which are also usedduring the clean step, where fluorine species are not rapidly removedand recombination does not occur. In the pre-clean stabilization step,chamber 15 is brought to a pressure between about 1-2 torr, preferablyabout 1.5 torr, with gate valve 280 is open. With chamber 15 maintainedat pressures lower than about 1-2 torr, rapid removal of fluorinespecies occurred, resulting in poor chamber cleaning results. At chamberpressures higher than about 1-2 torr, recombination may occur due tocollision losses, as well as causing overheating and damage toapplicator tube 292. Heater 25 is moved away from gas distribution plate20 to a distance of between about 450-700 mil, preferably about 600 mil.The clean gas, NF₃, is also introduced at a rate of between about600-1100 sccm, preferably about 950 sccm, into applicator tube 292. Thispre-clean stabilization step lasts between about 2-6 seconds, preferablyabout 3 seconds before microwave power is applied during the chamberclean step.

In the chamber clean step, the pre-clean stabilization conditions inchamber 15 are maintained at a pressure ranging between about 1-2 torr,preferably at about 2 torr. When the cleaning procedure is performed,microwave power of between about 500-2500 Watts is applied to applicatortube 292. Preferably, magnetron 711 provides about 2.45 GHz microwavesand is operated in CW mode at about 2100 Watts for the preferred cleangas flow of about 950 sccm. The microwaves are transmitted frommagnetron 711 through the waveguide and optimizing system to enterapplicator tube 292 through the window, as discussed above. UV lamp 731ignites the reactive gases in applicator tube 292 to form a plasma, withionization sustained by the microwave energy entering applicator tube292 at the window.

During the chamber clean step, fluorine radicals from the plasma formedin applicator tube 292 to which microwaves are applied may then flowthrough opened gate valve 280 and into chamber 15 to clean surfaces ofundesired oxide residues. Since the plasma is formed upstream of chamber15, only the reactive fluorine radicals in the plasma are able to reachand remove the residue built-up portions of chamber 15. Therefore,various portions of chamber 15 are cleaned of deposition processresidues while minimizing direct plasma damage to the chamber 15. Thechamber clean lasts between about 30 seconds to about 10 minutes,preferably between about 60-200 seconds, and most preferably for about160 seconds. Of course, the chamber clean time may vary depending on thethickness and type of oxide residue in chamber 15. As mentioned above,it is recognized that flow values may differ depending on the size andtype of the chamber, as well as the dimensions and material of theapplicator tube, used in other embodiments. The above-described cleanprocess also reduces backside undesired residue deposition behind boththe blocker and gas distribution plates.

After the chamber clean, additional post-clean steps may be performed.During the post-clean steps, chamber 15 is preferably maintained at theabove temperatures discussed for the above deposition and cleanprocesses. At the end of the chamber clean step, clean gas flow isstopped and microwave power is no longer supplied. Chamber 15 is pumpedto remove most of the F residue atoms. During this post-clean pumpingstep, heater 25 is moved to a position of between about 1500-2200,preferably about 2000 mil, from gas distribution plate 20 while thethrottle valve is opened and gate valve 280 remains open. The pumpingstep lasts between about 5-20 seconds, preferably about 10 seconds,depending on the amount of clean gas reactants and residue exhausted outof chamber 15. Clean endpoint detection system also may be utilized toassist in determining the stop time for the post-clean pumping untilsubstantially all deposition process residues are removed from chamber15.

After the fluorine-based chamber cleaning procedure, there may be someadsorption of active fluorine species on the surface of the chamberwalls, close to where the wafer would be located when the nextdeposition process occurs. In the next deposition process, the fluorinemight then interact or be incorporated into the deposited film, causingfilm sensitivity at the surface. This film sensitivity manifests itselfas a rough surface, which may be problematic with the tolerancesrequired by high integration devices, resulting in device malfunctions.The present invention provides the ability to getter any adsorbedfluorine from the surface of chamber walls by several methods discussedbelow.

After the post-clean pumping step, a seasoning may be performed torecombine all free F species by either chemical reaction or trapping theF to the chamber walls through silicon oxide (SiO₂) deposition. Thepost-clean pumping and seasoning steps are performed for reducing bothparticle formation and F content inside subsequently deposited films.

Optimally, between the post-clean pumping step and seasoning step isanother stabilization step to stabilize chamber pressure and gas flowand to move heater 25 into position for the seasoning step. In thisstabilization step, gate valve 280 is closed and chamber 15 ismaintained at a pressure of between about 20-70 torr, preferably 50torr. Heater 25 is also moved to a position of between about 300-550mil, preferably about 500 mil, from gas distribution plate 20. In aspecific embodiment, the seasoning step presently described uses ozoneand TEOS with helium as the carrier gas to season chamber 15 forsubsequent silicon oxide deposition. Of course, other gases may be usedin the seasoning and pre-seasoning stabilization steps, depending on thetype of silicon oxide deposition desired. In the pre-seasoningstabilization step, liquid TEOS at a flow rate of between about 200-400mgm, preferably about 300 mgm, is vaporized and transported with ahelium carrier gas flowing at a rate of between about 4000-8000 sccm,preferably at about 6000 sccm, into chamber 15. Gas flows may beintroduced into chamber 15 via the normal inlets used for deposition orvia applicator tube 292 without application of microwaves. Thisstabilization step lasts between about 5-25 seconds, preferably about 15seconds, before the seasoning step begins with the introduction of theoxygen source to begin deposition of the seasoning oxide onto chamber15. In the thermal seasoning step, ozone is introduced at the flow rateused for the particular deposition process used (e.g., about 5000 sccmfor the experimental USG deposition process at 550° C. discussed above,or about 4000 sccm for the experimental PSG deposition process at 600°C. discussed above) for between about 10-20 seconds, preferably about 15seconds, to deposit a thin layer of silicon oxide (e.g., theexperimental USG deposition process having about 12.5 wt % oxygen, orthe experimental PSG deposition process having about 8 wt % oxygen) ontosurfaces in chamber 15. During the seasoning step, the ozone flow isoptimally consistent with the deposition process to minimize anyfluctuation in ozone flow and concentration. Seasoning chamber 15thereby can trap fluorine atoms that may have been adsorbed onto thesurfaces of chamber 15.

Following the thermal seasoning step discussed above, finalstabilization and pumping steps may be performed. Optimally, these finalsteps are also performed at the deposition temperatures discussed above.In the final stabilization step, the throttle valve is openedperiodically to allow the chamber pressure to adjust to atmosphere,while gate valve 280 remains closed. Heater 25 is moved to a position ofbetween about 800-1000 mil, preferably about 999 mil, from gasdistribution plate 20. TEOS flow is stopped, while helium and ozoneflows remain the same as in the seasoning step. The final stabilizationstep is performed for a time period of between about 5-20 seconds,preferably about 10 seconds, before the final pumping step begins. Inthe final pumping step, gate valve 280 remains closed and heater 25 isnot moved. All gas flows are stopped and the throttle valve is opened.The final pumping step lasts between about 5-20 seconds, preferablyabout 10 seconds, before another wafer is introduced into chamber 15,which is now ready for the next deposition process, heating, or wafercleaning step. It is recognized that final stabilization and pumpingsteps also may be modified and similarly used with the particularseasoning step or alternative gettering step (examples discussed below)selected.

In embodiments alternative to those discussed above, the pre-cleanstabilization step discussed above may further include a ramping of themicrowave power from a low microwave power to the final clean operatinglevel of microwave power, allowing pre-clean stabilization of pressureand microwave plasma generation. In a preferred alternative embodiment,the pre-clean stabilization step discussed above may be substituted withthe following pre-clean stabilization.

Allowing for simultaneous stabilization of pressure and microwave power,the step of ramping up the microwave power to generate a N₂ (or otherinert gas, depending on the clean gas used) plasma provides a lowerpressure shock profile on applicator tube 292 upon NF₃ plasmageneration, in accordance with a specific embodiment. Microwave powerlevels applied to magnetron 711 from microwave power supply 110 may beadjusted under the control of processor 50. For example, the microwavepower may be ramped from zero to a level of about 300 Watts (or someother power level between 0 and the final clean operating power level)during the stabilization step, and then to 2100 Watts in the clean step,to provide a more gradual, optimal stabilization process. Specifically,after the heating step, heater 25 is moved to a position about 600 milfrom gas distribution plate 20 and N₂ is introduced at a flow of betweenabout 100-400 sccm, preferably about 300 sccm, into applicator tube 292,while the throttle valve remains open and gate valve 280 remains closed.After about 5 seconds, the throttle valve is closed and gate valve 280is opened, allowing pressure to stabilize for the next 5 seconds aschamber 15 is brought to the clean process pressure, about 1.5 torr in aspecific embodiment. Then, an intermediate level of microwave powerbetween about 200-400 Watts, preferably about 300 Watts, is applied toapplicator tube 292 to form a N₂ plasma during the next 5 seconds. Forthe next 5 seconds, NF₃ is also introduced into applicator tube 292while the microwave power level is ramped to the clean level.Specifically, NF₃ may be introduced at a rate between about 600-1100sccm, preferably about 950 sccm, into applicator tube 292, while themicrowave power level is ramped up to the final microwave power cleanoperating level of about 2100 Watts. Then, N₂ flow is stopped and plasmais generated using only NF₃, allowing for stabilization of the NF₃plasma generation stabilization for about 5 seconds. From this point,the clean may proceed, as discussed above. In the above discussedalternative embodiment, both pressure and plasma generation arestabilized prior to performing the cleaning step with the NF₃ cleaningplasma. This alternative pre-clean pressure/plasma stabilization maylast for a total time period preferably between about 20-30 seconds witheach power level ramp-up allotted an appropriate slice of time from thetime period. Accordingly, pressure shocks from an immediate, one-stepapplication of high microwave power (for example, from 0 to 2100 Watts)on applicator tube 292 are thus minimized, resulting in an enhancedlifespan for applicator tube 292.

Although the above described embodiment is a two-step power levelramp-up, other embodiments may have multiple-step ramp-ups (for example,from 0 to 300 to 1200 to 2100 Watts). Further, a microwave powerramp-down step optionally may be performed between the above describedclean step and the post-clean pumping step. Two-step or multiple-stepramp-downs also are possible for other embodiments. Of course, theramping may be continuous, a series of discrete steps, or a combinationthereof. For CVD systems which have a RF plasma system, ramp-up and/orramp-down of RF power levels may be performed for pre-cleanstabilization steps where an in situ plasma chamber clean is used, inaccordance with further embodiments. Although specific times arediscussed above for each part of the stabilization, in otherembodiments, the specific times may be varied and parts of thestabilization may be combined or eliminated to reduce time.

As an alternative to the thermal chamber seasoning discussed above, achamber seasoning may be employed which uses TEOS and O₂. Vaporized TEOSmay be introduced into chamber 15 via inlet 43 and gas mixing box 273 orusing the bypass passage in the lid. The O₂ is sent through applicatortube 292 for radiation (for example, between about 500-2100 Watts,preferably 2100 Watts) by microwaves from magnetron 711 of microwaveplasma system 55, to produce atomic oxygen. O₂ may be introduced intoapplicator tube 292 at a flow rate of between about 50-200 sccm,preferably about 100 sccm, while gate valve 280 is opened and chamber 15is maintained at a pressure of between about 1-2 torr, preferably about1.5 torr, and a temperature of between about 300-650° C., preferablybetween about 550-600° C. The atomic oxygen is able to react with theTEOS in chamber 15 to provide a microwave-enhanced chamber seasoning.Alternatively, for embodiments having a RF plasma system able to providean in situ plasma, vaporized TEOS may be introduced into chamber 15where the RF plasma system can create a plasma with which the atomicoxygen may react for a RF-enhanced chamber seasoning.

As another alternative to chamber seasoning to provide gettering offluorine atoms from chamber surfaces, SiH₄ may be flowed at a rate ofbetween about 50-200 sccm, preferably about 100 sccm, into chamber 15 topurge chamber 15. Silane may flow into chamber 15 via line 85 intochamber 15 from one of the other supply sources 90 (FIG. 1C) to gasmixing system 93 with closed gate valve 280, via other purge inlets tochamber 15 with closed gate valve 280, or via applicator tube 292 withor without application of microwaves and with opened gate valve 280.During the silane purge procedure, chamber 15 is maintained at apressure of about 1-5 torr and a temperature of between about 300-650°C., preferably between about 550-600° C., with gate valve 280 closed.Purging chamber 15 absorbs the F atoms and results in the formation ofSiF₄ gas, which is then pumped out of chamber 15 via the exhaust system.The endpoint detection system, as described above in detail, then allowsthe system to determine when the chamber cleaning process is completelydone.

As a further alternative to seasoning or to purging chamber 15 withsilane, as described above, gettering may be achieved by providingactive hydrogen into chamber 15. Hydrogen (e.g. H₂ or other hydrogensource) would be used as the "clean gas" supply source at a flow rate ofbetween about 50-200 sccm, preferably about 100 sccm, and sent viaswitching valve 105 into applicator tube 292 via inlet 57 (FIG. 1C).Magnetron 711 is operated at CW mode at a power level of between about500-2500 Watts, preferably about 1000 Watts, to provide microwave energyto applicator tube 292, thereby producing a plasma therein. The activehydrogen from the plasma in applicator 292 would then flow through thelined passage in enclosure assembly 200 and into conduit 47 for use inchamber 15. Of course, for systems which also include RF plasma systems,hydrogen may be introduced into chamber 15 and RF energy applied inchamber 15 to provide the active hydrogen. During the getteringprocedure, chamber 15 is maintained at a pressure of about 1-2 torr and,optimally, at the deposition temperature of about 300-650° C.,preferably between about 550-600° C. with gate valve 280 open. Theactive hydrogen reacts with the adsorbed fluorine to produce hydrogenfluoride (HF) vapor which may then be pumped out of chamber 15. Anendpoint detection system, operating on similar principles as theendpoint system described above but to detect changes in light intensitydue to absorbance by HF, may also be used.

Yet another alternative to seasoning, purging chamber 15 with silane, orusing active hydrogen, is to provide ammonia into chamber 15. Ammonia(NH₃) would be used as the "clean gas" supply source in gas panel 80 ata flow rate of between about 50-200 sccm, preferably about 100 sccm, andsent via switching valve 105 into applicator tube 292 via inlet 57 (FIG.1C). Magnetron 711 is operated at CW mode at a power level of betweenabout 500-2500 Watts, preferably about 1000 Watts to provide microwaveenergy to applicator tube 292, thereby producing a plasma therein. Theammonia from the plasma in applicator 292 would then flow through thelined passage in enclosure assembly 200 and into conduit 47 for use inchamber 15. During the gettering procedure, chamber 15 is maintained ata pressure of about 1-2 torr and, optimally, at the depositiontemperature of between about 300-650° C., preferably between about550-600° C. with gate valve 280 open. The ammonia reacts with theadsorbed fluorine to produce an ammonium fluoride compound and HF vaporwhich may then be pumped out of chamber 15. Of course, for systems whichalso include RF plasma systems, ammonia may be introduced into chamber15 and RF energy applied in chamber 15 to provide the ammonium fluoridecompound and HF. An endpoint detection system, operating on similarprinciples as the endpoint system described above but detecting lightintensity changes due to absorbance by ammonium fluoride and HF, mayalso be used.

Although the cleaning process conditions described above are exemplaryfor the present embodiment, other conditions may also be used. The abovedescription discusses NF₃, merely as an example, in a Giga Fill™ Centurachamber available from Applied Materials fitted for 200-mm wafers andhaving 6 liters total volume, as do the various deposition descriptionsbelow. However, other fluorine-containing or chlorine-containing gases,such as NF₃ and argon, NF₃ and N₂, NF₃ and O₂, NF₃ and atomic oxygengenerated by microwave plasma system 55, dilute F₂, CF₄, C₃ F₈, SF₆, C₂F₆, Cl₂, etc., may be used as well. Other gases besides those describedabove also may be used for the gettering procedure. Also, pre-seasoningstabilization steps would vary depending on the particular type ofseasoning/gettering process selected from the various alternatives tothe above discussed thermal seasoning. The above descriptions forcleaning, gettering, and seasoning are stated to occur at preferredtemperatures (for example, about 550-600° C.), but it is noted that,most preferably, chamber 15 is maintained at the same temperature atwhich the particular process is being run in chamber 15. Of course,different temperatures also may be used in other embodiments. Further,some embodiments may combine, add, or eliminate some portions of thecleaning, gettering, and seasoning steps described above.

III. Test Results and Measurements

A. Ultra-shallow Doped Junctions

To demonstrate the operation of the apparatus and method according toembodiments of the present invention, experiments were performedmeasuring the sheet resistivity and junction depths of ultra-shallowjunctions formed using as examples BSG films manufactured without a USGcapping layer and formed using BSG films with a USG capping layer. Theuncapped BSG films were about 150 Å thick, while the capped BSG filmswere about 150 Å thick with about a 200 Å USG cap. Both capped anduncapped BSG films were deposited on a low-resistivity N-type siliconwafer. Sheet resistivity and junction depths of ultra-shallow junctionsformed using the uncapped and capped BSG films were measured. For filmsdeposited in chamber 15 of CVD apparatus 10, described in detail above,gate valve 280 is closed during the film deposition steps according to aspecific embodiment. Actual process conditions used in the experimentsare as follows. Specifically, the BSG films were deposited at atemperature of about 500° C. and at a pressure of about 600 torr.Spacing between the susceptor and manifold was about 300 mil. Gas flowsin the experiments included introducing TEB into the chamber at a rateof about 200 mgm, introducing TEOS at a rate of about 500 mgm,introducing oxygen (O₃) at a rate of about 5000 sccm, and introducingthe helium carrier gas at a rate of about 8000 sccm.

The above conditions resulted in BSG film deposited at a rate of 700Å/minute. The deposited BSG film had a thickness of about 150 Å for aprocess time of about 15 seconds.

In experiments where a USG cap was used, the USG capping layer wasformed in an in situ process immediately after the bulk BSG layer wasdeposited. The preferred embodiments use a chamber that is a closedsystem which minimizes moisture available to react with the BSG filmbefore deposition of the USG capping film. The susceptor was heated to atemperature of about 500° C., the chamber was maintained at a pressureof about 600 torr, and the susceptor was positioned about 300 mil fromthe gas distribution manifold. TEOS, ozone and helium were introducedinto the deposition chamber at flow rates of about 500 mgm, 5000 and5000 sccm, respectively. The above conditions resulted in a USG filmdeposited at a rate of about 700 Å/minute. A USG film had a thickness ofabout 200 Å for a process time of about 15 seconds.

Diffusion of dopants from the uncapped and capped BSG fims is achievedby heating the film using annealing or a rapid thermal process. Forexample, a rapid thermal process for 60 seconds in a nitrogen (N₂)ambient may result in a junction depth of about 500-1000 Å depending onthe temperature, time and dopant concentration.

The parameters used in the experiments using BSG films should not belimiting to the claims as described herein. One of ordinary skill in theart can also use other chemicals, chamber parameters, dopants, andconditions to produce BSG films or other films such as PSG, AsSG, andothers.

Experiments were conducted using uncapped BSG films of about 200 Åthickness having about 6 wt % of boron. These experiments illustrate theability to form ultra-shallow junctions using BSG films as the dopantsource for a subsequent diffusion step.

At boron concentrations exceeding 6 wt % boron, uncapped BSG filmsdeposited at temperatures less than about 500° C. tended to becomeunstable and to crystallize within hours. As mentioned above,crystallization reduces the amount of boron atoms available fordiffusion into the silicon substrate. Deposition of BSG at temperaturesgreater than about 550° C. are believed to provide stable uncapped BSGfilms with boron concentration of more than 6 wt %. For applicationswhere boron concentrations greater than 6 wt % boron are needed, BSGfilms may be optimally capped with a USG film to preventcrystallization. By preventing outgassing, the USG cap also provides theability to control the direction of the diffusion of dopant atoms intothe silicon substrate. The USG cap therefore prevents more boron atomsfrom being lost so that more boron atoms are available for diffusionthat may be directed more easily into the silicon substrate.

To demonstrate the further advantages of using a capping layer over thedoped dielectric layer for some applications, further experiments wereconducted using BSG films having about a 150 Å thickness and a 6.131 wt% boron, with about a 200 Å USG cap deposited over the BSG film. Thesefurther experiments illustrate the ability to form ultra-shallowjunctions using capped BSG films as the dopant source for a subsequentdiffusion step. Sheet resistivity and junction depth of theultra-shallow junctions formed using uncapped and capped BSG films weremeasured. These experiments show that subjecting the BSG film to a 1minute rapid thermal process at about 1050° C. provides the capabilityto control the sheet resistivity and junction depth of ultra-shallowjunctions formed with either the BSG film alone or with the BSG filmwith USG cap.

FIGS. 22A-22C provide information about the effect of the USG cap on thejunction depth and dopant uniformity of the diffused regions.Measurements for FIGS. 22A and 22C were performed using solid statemeasurement equipment for the spreading resistance profiles, as is wellknown to those skilled in the art. Carrier concentration is shown as afunction of depth. A "p" represents the measured concentration of boronat a depth measured from the silicon substrate surface, and an "N"represents the measured concentration of the N type silicon substrate ata depth measured from the silicon substrate surface. The junction depthis defined as the position where the dopant concentration equals thesubstrate concentration. In the present experiments, the siliconsubstrate used had a substrate concentration of about 1.6×10¹⁴carriers/cm³. Sheet resistivity of the diffused regions shown in FIGS.22A and 22C was measured using four-point probe (4 pp) techniques, asare well known to those skilled in the art. FIG. 22B illustrates thetotal impurity profile of the wafer of FIG. 22A as measured by the moreelaborate method of secondary-ion-mass-spectroscopy (SIMS) which isuseful for providing precision profile measurements inhigh-concentration or shallow-junction diffusions, as is well known tothose skilled in the art.

Specifically, FIG. 22A is a graph showing the dopant profile of anultra-shallow junction formed after a heating step using a 6.131 wt %BSG layer having a USG capping layer. The BSG film was about 150 Å thickand the USG capping layer deposited on top of the BSG film was about 200Å thick. The heating step was performed by a rapid thermal process forabout 60 seconds at about 1050° C. The BSG and USG films were thenstripped by etching. As seen in FIG. 22A, the resulting junction has adepth of about 0.06 μm in the silicon substrate, and the dopant profileappears fairly uniform. The maximum concentration of boron is about6×10¹⁹ carriers/cm³. The sheet resistance of the resulting junction wasmeasured to be about 685 Ω/cm². The 4 pp sheet resistance was measuredto be about 222 Ω/cm², with the summation of dose ions in the P typelayer measured (Σp) being 1.6×10¹⁴ carriers/cm².

FIG. 22B illustrates the dopant depth profile as measured by SIMS for anultra-shallow junction described in FIG. 22A. From the surface of thesilicon substrate to a depth of about 100 Å from the surface, theconcentration of boron ranges between about 2×10¹⁸ carriers/cm³ to about1×10²¹ carriers/cm³. Between about 100 Å to about 300 Å from the surfaceof the silicon substrate, the concentration of boron ranges betweenabout 1×10²¹ carriers/cm³ to about 3×10²¹ carriers/cm³. Below about 300Å from the surface of the silicon substrate, the concentration of boron,silicon, and oxygen diminishes rapidly indicating the bulk substrate.The steep shallow junction shown in FIG. 22B demonstrates the dopantincorporation possible according to an embodiment of the presentinvention.

FIG. 22C is a graph showing the dopant profile of an ultra-shallowjunction formed without the heating step using a 6.131 wt % BSG layerhaving a USG capping layer. The BSG film was about 150 Å thick and theUSG capping layer deposited on top of the BSG film was about 200 Åthick. No heating step was performed. The BSG and USG films werestripped by an etching technique. As seen in FIG. 22C, it appears ajunction with a depth of about 0.025 μm has formed despite the lack of aheating step. Apparently, the junction has formed due to the high dopantconcentration of boron in the BSG film diffusing into the siliconsubstrate even without a heating drive-in step. The maximumconcentration of boron is about 7×10¹⁷ carriers/cm³. The sheetresistance of the resulting junction was measured to be about 55 Ω/cm²,with the summation of dose ions in the P type layer (Σp) being 4.9×10¹¹carriers/cm².

FIG. 23A is a graph showing the dopant profile of the junction formedwith a heating step using an 8.084 wt % BSG layer having a USG cappinglayer. FIG. 23B is a graph comparing the dopant profiles of thejunctions formed with the same heating step using a 6.131 wt % BSG layerhaving a USG capping layer and an 8.084 wt % BSG layer having a USGcapping layer, in order to illustrate the effect of dopant concentrationon junction depth. FIGS. 23C and 23D show the effect of the temperatureof the heating step on junction depth and on sheet resistivity,respectively. FIGS. 23E and 23F show the effect of the time of theheating step on junction depth and sheet resistivity, respectively. Thespreading resistance profiles and sheet resistivity measurements ofFIGS. 23A-23F were performed using solid state equipment and four-pointprobe measurements.

FIG. 23A is a graph showing the dopant profile of the junction formedwith a heating step using an 8.084 wt % BSG layer having a USG cappinglayer. The BSG film was about 150 Å thick and the USG capping layerdeposited on top of the BSG film was about 200 Å thick. A heating stepwas performed using a rapid thermal process for about 60 seconds atabout 1000° C. The BSG and USG films were stripped by an etchingtechnique. As seen in FIG. 23A, an ultra-shallow junction having a depthof about 0.12 μm was formed with good dopant uniformity. The maximumconcentration of boron is about 1×20³⁰ carriers/cm³. The sheetresistance of the resulting junction was measured to be about 145 Ω/cm²,with the summation of dose ions (Σp) being 7.9×10¹⁴ carriers/cm². The 4pp sheet resistance was measured to be about 96 Ω/cm².

FIG. 23B shows the dopant profiles of the junctions formed with aheating step using different boron wt % BSG layers (in particular 6.131wt % and 8.084 wt %) having USG capping layers. The BSG films were eachabout 150 Å thick and the USG capping layers deposited on top of the BSGfilms were each about 200 Å thick. The heating step performed was arapid thermal process for about 60 seconds at about 1000° C. As seen inFIG. 23B, the resulting junction depth for the 8.084 wt % BSG film isalmost twice as much as the resulting junction depth for the 6.131 wt %BSG film.

FIGS. 23C and 23D are graphs showing the effect of heating steptemperature on dopant profiles and sheet resistivity, respectively, for6.131 wt % BSG films having USG capping layers. The BSG films were about150 Å thick and the USG capping layers deposited on top of the BSG filmswere about 200 Å thick. The heating steps were performed using a rapidthermal process for about 60 seconds at temperatures of about 900° C.,950° C., 975° C., and 1000° C. As shown in FIG. 23C, the junction formedafter the heating step at 1000° C. is about 0.1 μm, compared to theabout 0.06 μm junction formed after the heating step at the lowertemperature 975° C. The sheet resistivity of the 6.131 wt % BSG film wasabout 180 Ω/cm² for the heating step at 1000° C., and about 600 Ω/cm²for the heating step at 975° C., as seen in FIG. 23D. A highertemperature heating step (beyond 950° C.) results in a deeper diffusiondepth for the shallow junction formed.

FIGS. 23E and 23F are graphs showing the effect of heating step time ondopant profiles and sheet resistivity, respectively, for 6.131 wt % BSGfilm having USG capping layers. The BSG films were about 150 Å thick andthe USG capping layers deposited on top of the BSG films were about 200Å thick. The heating step was performed using a rapid thermal process atabout 1000° C. for about 40 seconds and for about 60 seconds. As shownin FIG. 23E, the junction formed after about a 40-second heating step isabout 0.06 μm, while the junction formed after a 60-second heating stepis abut 0.1 μm. The sheet resistivity of the 6.131 wt % BSG films wasabout 230 Ω/cm² after the 40 second heating step and about 150 Ω/cm²after the 60 second heating step. Accordingly, it is seen that thelength of time of the heating step may determine the diffusion depth informing ultra-shallow junctions.

The above experiments of BSG used for ultra-shallow doped junctionformation are presented merely as examples to illustrate aspects of thepresent invention and should not be considered as limiting the scope ofthe present invention.

B. PSG for PMD Layer

To demonstrate the operation of the apparatus and method according toembodiments of the present invention, experiments were performed todeposit a PSG film, for example, as a PMD layer. Prior to the depositionof PSG film as the PMD layer, the wafer has typically been subjected tomultiple processing steps to form, for example, gate electrodes, oxidesidewalls, isolation trenches, etc. In the experiments, the PSG filmswere deposited in a resistively-heated Giga Fill™ Centura chamber (aclosed system having a total volume of about 6 liters and outfitted for200-mm wafers) manufactured by Applied Materials, Inc.

In the experiments, pre-deposition steps were performed to bring chamber15 to the desired deposition pressure and to stabilize the gas/liquidflows before depositing the PSG film as a PMD layer on a wafer. Ofcourse, it is recognized that pre-deposition steps may be varied fromthe below description (which is merely an exemplary specificembodiment), as is optimal for different deposition recipes. Thepre-deposition steps reduce unnecessary deposition on chamber walls andalso contribute to yielding uniform depth profiles for the depositedfilms. Before any pre-deposition steps occur, a wafer is loaded invacuum chamber 15 onto heater 25 through the vacuum-lock door, which isthen closed. Heater 25 is heated up to the processing temperature ofabout 600° C., which is maintained throughout the pre-deposition steps,the deposition step and the post-deposition steps.

In a first pre-deposition step, heater 25 is at a position about 600 milfrom gas distribution plate 20. With the throttle valve open for about 5seconds, helium at a flow rate of about 4000 sccm, and O₂ at a flow rateof about 2900 sccm are introduced into chamber 15. The neutral gases,helium and O₂, are introduced first into chamber 15 for their flow ratesto stabilize. These flow rates of helium and O₂ are maintainedthroughout the pre-deposition steps.

In the second pre-deposition step, the throttle valve is closed and thepressure in chamber 15 is increased to the deposition pressure. Thesecond pre-deposition step lasts about 30 seconds and allows thepressure, which may initially fluctuate somewhat around the desireddeposition pressure, to stabilize in chamber 15. Heater 25 is moved tothe processing position of about 330 mil from gas distribution plate 20in second pre-deposition step.

In the third pre-deposition step, when the pressure in chamber 15 hasstabilized to the deposition pressure of about 450 torr, liquid TEOS isintroduced to allow stabilization of TEOS and helium flow. With the TEOSflow rate at about 1000 mgm, the vaporized TEOS gas mixes with thehelium carrier gas for about 3 seconds during the third pre-depositionstep, before the deposition step.

Having stabilized the chamber pressure, temperature, and TEOS/helium gasflows, and adjusted the position of heater 25, deposition processing canbegin. At the onset of the deposition step, O₂ flow is terminated.Liquid TEPO is introduced at a rate of about 24 mgm, and O₃ (about 8 wt% oxygen) is introduced at a rate of about 4000 sccm. Being liquids, theTEPO and TEOS sources are vaporized by the liquid injection system andthen combined with the inert carrier gas helium. This mixture isintroduced into chamber 15 from gas distribution plate 20 to supplyreactive gases to the wafer surface where heat-induced chemicalreactions take place to produce the desired PSG film. The aboveconditions result in a PSG film deposited at a rate of about 1780Å/minute. By controlling the deposition time, a PSG film having athickness of about 5300 Å is formed at the process conditions describedabove in about 404 seconds. The wt % of phosphorus in the resulting PSGfilm is about 4 wt %.

After deposition, a termination step is performed that is optimizes thestability of the deposited PSG film to provide moisture andcrystallization resistance. In the termination step, which lasts forabout 3 seconds, the deposition conditions are maintained while TEPOflow is terminated. The termination step therefore deposits a USGcapping layer in an in situ manner in chamber 15, by the gas terminationmethod discussed above. The USG layer is very thin compared to thethickness of the bulk PSG film.

After the PSG deposition and USG deposition steps, post-deposition stepsare utilized to control the ramping down of chamber pressure and tocontrol gas shut-off. By adjusting the pressure and gas shut-off, thepost-deposition steps help reduce particle formation which otherwise cancause wafer contamination and damage.

In a specific embodiment, three post-deposition steps were used. In thefirst post-deposition step immediately following the above terminationstep, TEOS flow is terminated while heater 25 is moved into a positionabout 600 mil from gas distribution plate 20. Also, the throttle valveis opened periodically to allow chamber pressure to gradually ramp downduring the first post-deposition step, which lasts about 15 seconds. Inthe second post-deposition step, the throttle valve is openedperiodically to ramp down chamber pressure for the third post-depositionstep (the pumping step), as helium flow into chamber 15 is terminated bypumping it through a bypass valve. Heater 25 is also moved lower to aposition about 999 mil from plate 20 during the second post-depositionstep, which lasts about 15 seconds. In the third post-deposition step,which lasts about 3 seconds, the throttle valve is opened and O₃ flowinto chamber 15 is terminated by pumping it through a final valve.

The above experimental conditions for the deposition of PSG suitable forbeing used as a PMD layer are optimal to provide the best film qualitywith high throughput. By enhancing surface diffusion at increasedsurface temperature, the thermal PSG film deposited using the TEOS/O₃chemistry at temperatures of about 600° C. exhibited excellent stepcoverage, more cross-linked structure, and more stable oxidizationstructure for P and Si, which yielded excellent film quality. Thedeposited PSG film was high quality in terms of flow-like step coverage,high moisture resistance, high breakdown voltage, smooth surface, nosurface damage (i.e., plasma damage), and no fixed charge. The depositedPSG film exhibited good film thickness uniformity. Specifically, filmthickness uniformity (49 pt., 1 σ) at about 1.2 μm thickness of thedeposited PSG film was measured to be less than about 1.5.

FIG. 24A is a photomicrograph demonstrating the as-deposited gap fillcapabilities of PSG films deposited at 600° C. in accordance with aspecific embodiment of the present invention. In particular, the PSGfilm deposited at 600° C. was shown to be capable of filling high aspectratio gaps having a height (h) and a spacing (w) without the formationof voids, as seen in FIG. 24A. FIG. 24B is a simplified diagram (notshown to scale) of a section of the integrated circuit structure shownin FIG. 24A. As seen in FIG. 24B, substrate 1200 has stacked gatestructures, specifically electrodes 1220 with tungsten silicide (WSi)caps 1240, formed thereon. An oxide layer 1260 is deposited onto stackedgate structures to form high aspect ratio gaps with h of about 0.35 μmand w of about 0.08 μm shown by dotted lines, as seen in FIGS. 24A-24B.FIG. 24A therefore demonstrates an exemplary structure with high aspectratio (about 4.3:1) gaps that are filled by PSG film 1280, which is usedas a PMD layer. Deposited at about 600° C. using the preferred recipediscussed above, PSG film 1280 exhibits excellent high aspect ratio gapfill capability without the need for a reflow typically done at about750-800° C., which is often inconsistent with increasingly tight thermalbudgets.

In addition to having excellent gap fill capability for high aspectratios, PSG films deposited at about 600° C. advantageously are densefilms that exhibit high resistance to moisture absorption. Moistureabsorption of the deposited PSG film deposited was measured usingconventional Fourier Transform Infrared spectroscopy (FTIR) techniques,as are well known to one of ordinary skill in the art. FIG. 25illustrates the FTIR spectra of a PSG film deposited at about 600° C.under the following exemplary process conditions. According to aspecific embodiment, the exemplary process conditions include TEOS flowof about 1000 mgm, TEPO flow of about 24 mgm, helium flow of about 6000sccm, and ozone (about 12 wt % oxygen) flow of about 4000 sccm, at apressure of about 400 torr and spacing of about 330 mil between heater25 and gas distribution plate 20. The PSG deposition time was about 600seconds. As seen in FIG. 25, the FTIR spectra of the PSG film depositedat about 600° C. demonstrated no water spikes indicating moistureabsorption, and no measurable change in moisture absorption was seenover about 155 hours after deposition, illustrating the PSG filmstability over extended periods.

As demonstrated by FIG. 25, the deposited PSG film is dense, resistantto absorbing moisture. Deposition of a PSG film at high temperatures,for example at about 600° C., tends to drive out any moisture that mightbe absorbed into the film, resulting in a dense film. As a dense film,the PSG film deposited at high temperature has the advantage of notrequiring an additional step for further densification of the film. Thedense nature of the deposited PSG film makes it compatible for use as aPMD layer which can be planarized either by a subsequent anneal at atemperature greater than about 1000° C., or preferably by a CMP step. Inaddition to moisture absorption resistance, the present PSG filmdeposited at high temperatures is able to provide good film thicknessuniformity, as well as good gap fill without formation of voids or weakseams that can cause subsequent device problems. The high temperaturePSG film is particularly useful as a PMD layer as it provides goodphosphorus incorporation (between about 2-8 wt % phosphorus), which isimportant for gettering or trapping mobile ions such as sodium (Na+)ions that might otherwise migrate and cause shorting in the device.

The above description of experiments depositing and measuringcharacteristics of the deposited PSG film demonstrates its suitabilityfor use, for example, as a PMD layer. However, the description shouldnot be considered as limiting the scope of the invention.

C. USG for Oxide Filling Layer in Shallow Trench Isolation

To demonstrate the operation of the apparatus and method according toembodiments of the present invention, experiments were performed todeposit a USG film, for example, as a high quality oxide filling layerfor shallow trench isolation. Prior to the deposition of USG film as thehigh quality oxide filling layer, the wafer has typically been subjectedto multiple processing steps to form, for example, gate electrodes,oxide sidewalls, isolation trenches, etc. In the experiments, the USGfilms were deposited in a resistively-heated Giga Fill™ Centura chamber(a closed system having a total volume of about 6 liters and outfittedfor 200-mm wafers) manufactured by Applied Materials, Inc.

In the experiments, pre-deposition steps were performed to bring chamber15 to the desired deposition pressure and to stabilize the gas/liquidflows before depositing the USG film as a filling layer on a wafer. Ofcourse, it is recognized that pre-deposition steps may be varied fromthe below description (which is merely an exemplary specificembodiment), as is optimal for different deposition recipes. Thepre-deposition steps reduce unnecessary deposition on chamber walls andalso contribute to yielding uniform depth profiles for the depositedfilms. Before any pre-deposition steps occur, a wafer is loaded invacuum chamber 15 onto heater 25 through the vacuum-lock door, which isthen closed. Heater 25 is heated up to the processing temperature ofabout 550° C., which is maintained throughout the pre-deposition steps,the deposition step and the post-deposition steps.

In a first pre-deposition step, heater 25 at a position about 600 milfrom gas distribution plate 20. With the throttle valve open for about 5seconds, helium at a flow rate of about 7000 sccm, and O₂ at a flow rateof about 2900 sccm are introduced into chamber 15. The neutral gases,helium and O₂, are introduced first into chamber 15 for their flow ratesto stabilize. These flow rates of helium and O₂ are maintainedthroughout the pre-deposition steps.

In the second pre-deposition step, the throttle valve is closed and thepressure in chamber 15 is increased to the deposition pressure. Thesecond pre-deposition step lasts less than about 40 seconds and allowsthe pressure, which may initially fluctuate somewhat around the desireddeposition pressure, to stabilize in chamber 15. Heater 25 is moved tothe processing position of about 350 mil from gas distribution plate 20during the second pre-deposition step.

In the third pre-deposition step, when the pressure in chamber 15 hasstabilized to the deposition pressure of about 600 torr, liquid TEOS isintroduced to allow stabilization of TEOS and helium (or nitrogen) flow.With the TEOS flow rate at about 2000 mgm, the vaporized TEOS gas mixeswith the helium (or nitrogen) carrier gas for about 5 seconds during thethird pre-deposition step, prior to the deposition step.

Having stabilized the chamber pressure, temperature, and TEOS/helium gasflows, and adjusted the position of heater 25, deposition processing canbegin. At the onset of the deposition step, O₂ flow is terminated whileO₃ (about 12.5 wt % oxygen) is introduced at a rate of about 5000 sccm.Being liquid, the TEOS source is vaporized by the liquid injectionsystem and then combined with the inert carrier gas helium. This mixtureis introduced into chamber 15 from gas distribution plate 20 to supplyreactive gases to the wafer surface where heat-induced chemicalreactions take place to produce the desired USG film. The aboveconditions result in a USG film deposited at a rate of about 1450Å/minute. By controlling the deposition time, a USG film having athickness of about 10000 Å is formed at the process conditions describedabove in about 414 seconds.

After USG deposition, a purge step is performed that is optimizes thestability of the deposited USG film to provide moisture resistance. Inthe purge step, which lasts for about 3 seconds, the depositionconditions are maintained while TEOS flow is terminated.

After the USG deposition step and purge step, post-deposition steps areutilized to control the ramping down of chamber pressure and to controlgas shut-off. By adjusting the pressure and gas shut-off, thepost-deposition steps help reduce particle formation which otherwise cancause wafer contamination and damage.

In a specific embodiment, three post-deposition steps were used. In thefirst post-deposition step immediately following the above terminationstep, the carrier gas flow into chamber 15 is terminated by pumping itthrough bypass valve. Heater 25 is moved into a position about 600 milfrom gas distribution plate 20, as the throttle valve is openedperiodically to gradually ramp down chamber pressure during the firstpost-deposition step, which lasts about 15 seconds. In the secondpost-deposition step, the throttle valve is opened periodically tocontinue ramping down chamber pressure, and O₃ flow into chamber 15 iscontinued. Heater 25 is also moved lower to a position about 600 milfrom plate 20 during the second postdeposition step, which lasts about15 seconds. In the third post-deposition step, which lasts about 3seconds, the throttle valve is opened and O₃ flow into chamber 15 isterminated by pumping it through a fmal valve.

The above experimental conditions for the deposition of USG suitable forbeing used as a high quality oxide filling layer for shallow trenchisolation are optimal to provide the best film quality with highthroughput. In shallow trench isolation applications, the deposited USGfilm should be capable of void-free gap fill (typically at a nominalangle of about 85°), in addition to being a very dense and uniform film.The deposited USG film exhibited good film thickness uniformity.Specifically, film thickness uniformity (49 pt., 1 σ) at about 5000 Åthickness of the deposited USG film was measured to be less than about1.5.

FIGS. 26A and 26B are photomicrographs demonstrating the relative gapfill capabilities of TEOS/O₃ USG films deposited at about 400° C. andabout 550° C., respectively, after reflow at about 1050° C. and a 6:1buffered oxide etch (BOE), in accordance with a specific embodiment ofthe present invention. In particular, FIG. 26A illustrates a trenchstructure having about 0.35 μm width and about 0.70 μm depth (about 2:1aspect ratio gap) with a filling layer that is a USG film deposited atabout 400° C. after a reflow at about 1050° C. FIG. 26A shows largevoids in the deposited USG film, indicating that the USG film depositedat about 400° C. is not very dense and appears to have been prone toshrinkage. Even after a reflow at a temperature above about 1000° C.,which can densify a USG film to some extent, the USG film deposited atthe temperature of about 400° C. is not very dense and does not survivethe high temperature anneal or a subsequent wet etch processing withoutopening up voids. In comparison, FIG. 26B shows a trench structurehaving about 0.18 μm width and about 0.45 μm depth (about 2.5:1 aspectratio gap) with a void-free filling layer that is a USG film depositedat about 550° C. after a reflow at about 1050° C. and a subsequent wetetch processing. The USG film deposited at about 550° C. is capable offilling high aspect ratio gaps without the formation of voids afterreflow, unlike USG films deposited at 400° C., as seen from FIGS. 26Aand 26B. After etch processes at very uniform etch rates, USG filmsdeposited at about 550° C. retain their superior step coverage withoutopening up voids.

As further evidence of the high aspect ratio gap filling capability ofUSG films deposited at about 550° C., FIG. 27 is a photomicrographdemonstrating the gap fill capability of the deposited USG film after ananneal at about 1000° C. and a subsequent wet etch processing, inaccordance with a specific embodiment of the present invention. FIG. 27shows a trench structure having about 0.16 μm width and about 0.48 μmdepth (about 3:1 aspect ratio gap) with a filling layer that is a USGfilm deposited at about 550° C. after a reflow at about 1000° C. Thetrench structure of FIG. 27 has a smaller spacing and a higher aspectratio than the trench structures shown in FIGS. 26A and 26B,illustrating the superior gap filling capability of the USG filmdeposited at about 550° C.

In addition to having excellent gap fill capability for high aspectratios, USG films deposited at about 550° C. advantageously are densefilms that exhibit high resistance to moisture absorption. Moistureabsorption of the deposited USG film deposited was measured usingconventional FTIR techniques. FIG. 28 illustrates the FTIR spectra of aUSG film deposited at about 550° C. under the following exemplaryprocess conditions, according to a specific embodiment. According to thespecific embodiment, the exemplary process conditions include TEOS flowof about 2000 mgm, helium flow of about 7000 sccm, and ozone (about 12.5wt % oxygen) flow of about 5000 sccm, at a pressure of about 600 torrand spacing of about 350 mil between heater 25 and gas distributionplate 20. As seen in FIG. 28, the FTIR spectra of the USG film depositedat about 550° C. demonstrated low moisture absorption (less than about 1wt % moisture). Further, FIG. 28 also illustrates that a moistureincrease of less than about 0.5 wt % moisture in the USG film was seenover about 160 hours after deposition, indicating the stability of theUSG film over extended periods.

Accordingly, as supported by FIG. 28, the deposited USG film is dense,resistant to absorbing moisture. Deposition of a USG film at hightemperatures, for example at about 550° C., tends to drive out mostmoisture that might be absorbed into the film, resulting in a densefilm. As a dense film, the USG film deposited at high temperatures of atleast about 550° C. has the advantage of being less prone to shrinkagethat might result in void formation after an annealing step and asubsequent wet etch processing, compared to USG films deposited at lowertemperatures. The dense nature of the deposited USG film makes itcompatible for use as a high quality oxide layer for filling trenchesused in shallow trench isolation applications. Due to its high density,USG films deposited at high temperatures and used as oxide fillinglayers can be planarized by either a subsequent anneal or a CMP step,with minimized likelihood of opening up voids. In addition to moistureabsorption resistance and good film thickness uniformity, the presentUSG film deposited at high temperatures provides excellent high aspectratio gap fill without formation of voids or weak seams that can causesubsequent device problems.

In general, high pressure O₃ /TEOS USG films may exhibit pattern orsurface sensitivity effects, resulting in uneven deposition, which isundesirable. It has been seen that problems with uneven deposition areworsened with higher O₃ /TEOS ratios. Advantageously, deposition of USGfilms at high temperatures such as at least about 550° C. requires useof more TEOS in order to achieve adequate deposition rates. Accordingly,the O₃ /TEOS ratio of USG films deposited at high temperatures is low(less than about 5:1), thereby eliminating any pattern or surfacesensitivity effects. Moreover, the film quality (e.g., density,shrinkage, etc.) is high for USG films deposited at high temperatures.Because of the high density of these high temperature deposition USGfilms, plasma densification treatments or plasma oxide caps are notneeded, thereby avoiding any plasma damage to the wafer. The lack of aplasma from such treatments in the chamber thus reduces possibility ofmetal contamination and potential shorting of devices in the wafer.Compared to low temperature thermal USG films, which often require aplasma densification treatment or plasma oxide cap and may shrink toopen voids after an anneal, thermal USG films deposited at temperaturesof about 550° C. exhibit excellent gap fill capability, minimalshrinkage, and uniform film density, and low metal contamination,without plasma damage, in accordance with the present invention.

The above description of experiments demonstrates the suitability of thedeposited USG film for use, by way of example, as a high quality oxidelayer for filling high aspect ratio trenches for shallow trenchisolation. The same CVD apparatus also may be used to deposit USG filmsat temperatures lower than 500° C. for IMD applications. Of course, theabove description should not be considered as limiting the scope of theinvention.

It is to be understood that the above description is intended to beillustrative and not restrictive. Many embodiments will be apparent tothose of skill in the art upon reviewing the above description. By wayof example, the inventions herein have been illustrated primarily withregard to a USG, BSG, PSG, and BPSG process recipes, but they are not solimited. For example, the dielectric film formed according to otherembodiments may be an arsenic doped silicon oxide film, or other dopedfilm. As another example, the deposition of dielectric films has beendescribed using carrier gas such as helium, but other carrier gases likeargon or nitrogen, may be used as well. As a further example, dielectriclayers have been described for particular applications, including dopedjunction formation, PMD layers, IMD layers, oxide filling layers,capping layers, etc. Of course, it is recognized that the same CVDapparatus discussed above may be used to deposit dielectric layers attemperatures lower than about 400° C., as well as temperatures above500° C. Additionally, various aspects of the present invention may alsobe used for other applications. Those skilled in the art will recognizeother equivalent or alternative methods of depositing the dielectriclayer while remaining within the scope of the claims of the presentinvention. The scope of the invention should, therefore, be determinednot with reference to the above description, but should instead bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

What is claimed is:
 1. A method comprising:flowing one or more processgases into a substrate processing chamber to deposit a layer on asubstrate; applying power to a heater for heating the heater to apredetermined target temperature, where an amount of power applied is afunction of a temperature ramp rate error based on a difference betweena desired ramp rate and a calculated ramp rate of heater temperature,said calculated ramp rate changing as a function of a currenttemperature of the heater at a point in time during heating; anddischarging exhaust gases from the substrate processing chamber.
 2. Themethod of claim 1 wherein the predetermined target temperature is atleast about 500° C.
 3. The method of claim 1 wherein the predeterminedtarget temperature is at least about 650° C.
 4. The method of claim 1wherein the applying step further comprises:measuring said currenttemperature of the heater within the substrate processing chamber duringsaid heating of the heater; determining the desired ramp rate based onthe current temperature of the heater; and wherein the power applied tothe heater is also a function of the desired ramp rate.
 5. The method ofclaim 4 further comprising steps of:using a control function based onthe temperature ramp rate error to determine an appropriate level ofsaid power to apply to the heater.
 6. The method of claim 5 furthercomprising steps of:dampening a system response of the heater to theappropriate level of said power using a saturation function if adifference between the appropriate level and a preceding level exceedssaturation limits; and wherein the appropriate level is determined usingthe control function when the difference between the appropriate leveland the preceding level is within saturation limits.
 7. The method ofclaim 6 wherein the dampening step is carried out by determining amaximum difference in power between adjacent time steps and limiting thedifference between the appropriate power and the preceding power to themaximum difference.
 8. The method of claim 5 wherein the calculated ramprate is determined based on a numerical differentiation technique. 9.The method of claim 8 wherein the calculated ramp rate is determinedbased on averaging measured ramp rates divided by an update period. 10.The method of claim 4 wherein the step of applying power is carried outby applying electrical energy to a resistive heater within the substrateprocessing chamber.
 11. The method of claim 4 wherein the currenttemperature is measured with a thermocouple.
 12. The method of claim 4wherein the desired ramp rate is determined by defining the desired ramprate as a continuous function of the current temperature of the heater.13. The method of claim 4 wherein the determining step occurs only onceduring said heating of the heater.
 14. The method of claim 4 whereinsaid step of determining the desired ramp rate occurs at a frequencybased on a defined time interval.
 15. The method of claim 14 wherein thedetermining step occurs at least about 10 times per second.
 16. Themethod of claim 1 wherein the heater comprises a ceramic material. 17.The method of claim 16 wherein the ceramic material comprises aluminumnitride.
 18. The method of claim 1 comprising:determining a temperatureerror between a predetermined target temperature and the currenttemperature of the heater during said heating of the heater.
 19. Themethod of claim 18 further comprising selecting a ramp control algorithmto determine an appropriate level of said power to apply to the heater,based on when said temperature error is greater than a predeterminedboundary value.
 20. The method of claim 18 further comprising selectinga temperature regulator algorithm when the temperature error is lessthan a predetermined boundary value, the temperature regulator algorithmusing proportional, integral, and differential (PID) control todetermine the appropriate level of said power.
 21. The method of claim 1wherein the applying step comprises selecting a desired ramp rate thatis a constant value based on a minimum thermal shock resistance of theheater.
 22. The method of claim 1 wherein said method is used to form anintegrated circuit device.
 23. A method comprising:measuring a currenttemperature within a processing chamber of a substrate processingapparatus; determining a temperature error between a predeterminedtarget temperature and said current temperature; selecting a rampcontrol algorithm to determine an appropriate power to control thetemperature within the processing chamber to said predetermined targettemperature, based on said temperature error being greater than apredetermined boundary value; selecting a temperature regulatoralgorithm when said temperature error is less than said predeterminedboundary value; and applying said appropriate power to control thetemperature within the substrate processing apparatus.
 24. A methodcomprising:measuring a current temperature of a heater within asubstrate processing chamber during substrate processing; determining adesired ramp rate based on the current temperature of the heater duringprocessing; and applying power to the heater based on the desired ramprate to control the temperature to said predetermined targettemperature, wherein a controller used to control the power has asaturation function adapted to limit the maximum allowable change inapplied power from one time step to a next time step.
 25. A methodcomprising:flowing one or more process gases into a substrate processingchamber to deposit a layer on a substrate; heating the chamber byapplying power to a heater, wherein the power applied to the heaterduring said heating is determined by using a temperature ramp controlalgorithm independent from a timed temperature trajectory; anddischarging exhaust gases from the substrate processing chamber.
 26. Amethod as in claim 25 wherein the heating step comprises calculating atemperature ramp rate error based on a desired temperature ramp rate andan actual temperature ramp rate of the heater.
 27. A method as in claim25 wherein the heating step comprises using a numerical differentiationtechnique.
 28. A method as in claim 27 wherein the numericaldifferentiation technique comprises comparing an average of a pluralityof measured temperatures in one power update period to an average of aplurality of measured temperatures from a previous power update period.